Hello, I'm a freelance programmer myself. Not exactly the same situation but I believe that I have some advice that applies to any and all forms of freelancing and "self marketing" so to speak. I'm going to list out some points of importance from my personal experiences both as a freelancer looking for work and a buyer who outsources work to other freelancers. Most of these points are equally as important as each other so don't think the order that I say them relates to a specific path or road to success. More so consider it as a bulleted list of things that will increase your chances.
Ok, I know I said everything is pretty equal but this one here is by far the MOST important tool in a freelancer's arsenal. You absolutely 100% need a portfolio showing lots of examples of your work. Many buyer's don't know any better, they know that there are thousands of freelance musicians out there, they think it's easy and that anyone who says "I can do it" can do it. After they get burned once or twice they will be looking for examples of you getting a LOT of work done not just one or two amazing tracks.
This one I mention because I noticed you have not filled out your profile here. Buyers look at this as a lack of dedication or care. I know this is Game Dev and not a freelance service and your not marketing here to get potential work but you are discouraging people that are looking to buy assets. We are all game developers or at the least aspiring game developers here. Although we may go to the Unity store to buy premade assets or we might look on freelancer.com to hire project based contractors but on the same note many people are associating your name with lack of dedication and care. If your other site's profiles reflect this at well it is more likely that interested buyers don't think you will actually complete the job. It is VERY important that everywhere you post on the internet shows your attention to detail and drive.
You linked a pretty nice loopable track that shows us that you have created... One track. This is good as that it does show your quality of work but it doesn't really make people think that you do this on a regular basis. It's more important to a potential buyer (at least the serious ones) that you get acceptable quality work done in a timely manner than it is that your work is perfect. Post more and make it easier for people to get to your examples of work everywhere. Do you have a range of talent? Can you do action / rock styled tracks? Can you do classical? Would you be a good fit for a mystery game? These are questions whose answers are normally answered at a glance depending on what you show us not what we go to find.
This is another really really big one. Buyers want to talk to you, they want to see things you have said to others, they want to see that you are capable of good and quick communications. This is actually easy to demonstrate and forums are the beginning of this. Post on forums, A LOT!. The more you post the more people start paying attention and the more they remember "hey it's easy to talk to that guy". Get more active on as many forums as you can keep up with.
Make it easy to find you:
Coming back to the portfolio and profile ideas. Many people are spoiled by the speed and abundance of information on the internet. Anything you ever want to know is normally a quick google away. We tend to get trumped pretty quick when a potential buyer finds it easier to get to someone else's site, portfolio or profile. I don't mean to suggest you should spam links all over the place but you should always make sure that your link's are available on every post that you make everywhere. For example, I'm in the position to recruit a composer right now for one of my clients (sorry but I already contracted him). However the point here is that if I hadn't found who I was looking for yet I couldn't have even tried to consider you because I have nothing to show my client (I can't find any more than the one song you posted).
Contribute don't spam:
You never know who a potential buyer is in this world. Like the above example that just a week ago I was a potential buyer is a great example. You may have never thought that Game Dev would make a connection that could lead to requests but you shouldn't ignore the possibility. Game Dev is a bit of a bad example because we are game developers or aspiring game developers here, it's pretty obvious that people here will be looking to buy assets at some point in their career. The important thing to remember is that you want to make it obvious that you are available without outright spamming about it. The easiest way to do this is to contribute and participate on different forums and sites, and make sure that your link is in the signature. You will quickly be amazed at how much traffic exponentially increases as your link appears in quality contributions to sites. Again I don't mean to make this about me but take head in the fact that I'm talking to you about freelancing your audio works making very little mention of my programming. However I know that at least 3 people that read this thread will click on my site and see who I am and what I do. (I run analytic's on my site and I see how much traffic Game Dev and Facebook drive in.. It's more than google).
So in recap what I'm saying it's not just about where you advertise yourself but how you advertise yourself and how much dedication you show. It may or may not be true that your offering your services over a poor medium but it might also be that your being out shined so to speak. The remedy for this is one of the hardest things you will ever do and it involves not sleeping. I assume you like everyone else have a day job, have a family and responsibilities. I know you can't spend every waking moment at your computer making things happen but you absolutely must find time every single day to make progress. You 100% need to get your profiles updated, you need to display your portfolio everywhere, you need to talk more and build reputation. Selling yourself as a freelancer is less about buying an ad on a website or getting into Google's adsense rotation. It's getting people to know you, getting people to talk about you, getting people to see (or in your case listen) to your works. The little known or at least little discussed fact is that completing things is more important than quality. I'm sure people will argue this and I should mention that you can consider this my opinion less than fact but I have seen this time and time again. I know very very high quality artists (I mean like they should be working for square soft they are so good). Guess how much they freelance? Never, they are flipping burgers. I also know some artists that maybe shouldn't even be called artists. Granted they are better than I but they're quality is very poor but they have hundreds of completed sprites, models, interfaces and other assets. How much work are they getting? So much I barely get to talk to them anymore.
I believe (it's my opinion) that completing work is more important to buyers than having the best quality. Although they will not pay for absolute crap, they will pay for someone half as good as you who can show lots of completed jobs. As a freelancer getting started this is difficult to overcome, your facing off against others who may have been doing it for years and they have dozens of completed works. How do you start getting your foot hold and making yourself a consideration? Do stuff. Do lots of stuff. Complete stuff. Talk to people. Pay attention to details like profiles and portfolios. Show the buyer you do things, it will make or break the sale almost every time. The less they see you have done both musically and contributorily the less faith they have that you will do something for them. I hope that this is a grossly incorrect assumption I am making and that your response is something along the lines of "Here's my portfolio with 300 demo tracks, here's my profiles on every other service everyone 100% complete". At which point you'r looking more at nsmadsen's points that you're probably just advertising in the wrong places and it's time to look for more outlets. If my assumptions are right and you don't have very many demo tracks (maybe because they don't sound so great and you don't want to show them), maybe you haven't been wasting your time on profiles because no one checks them (false that's the second thing I did, clicked the song came back and clicked your name), then I suggest you address these concerns immediately (like yesterday).
Again I must make the final note that I am speaking from my experiences. I am mentioning things that have made a difference in my career. I am not saying that these are absolute facts or that you will have the same experiences. I'm not a teacher, I'm not a sociology expert or anything of the sort. Take my words however you want, try it my way only if you want to. If it does make a difference well I'm glad that you found the same networks that I did. If it doesn't? Oh well at least you got experience in a few things that do relate to what your trying to do. However do not think that what I say is a definitive answer on how you get work as a freelancer.