I can't really offer advice on any other communities that will be better suited - my experience is that they're already relatively similar to the ones you've already listed, or worse. The GameDev Show and Test group (and it's related groups) on Facebook, in particular, is ridiculously hit and miss; I find it's mostly just people advertising their own stuff with no real interest in trying others' work, and unless you get lucky or you're making a meme game you probably won't get much engagement there.
I can't really comment on Itch, although I've heard some people have luck there. GameJolt is also often mentioned, and I believe is fairly similar to Itch.
Speaking for this community, I think blogs -- especially if they're regularly updated -- usually get more feedback than topics in the announcements forum. Setting up a Project and linking a blog so that updates feed through can get some good exposure due to the social media feeds. Focused questions in relevant forums (such as Game Design) can also get good input, as I've seen you already do from time to time.
With all of that being said, when you're after actual playtesting my impression is that it's generally difficult everywhere, and there's no particular community where people are more engaged and likely to download and give feedback on a game unless you already have your own established fan base eagerly following your work. Obviously it's not the same or as good as actual playtesting for some purposes, but I think including plenty of media (screenshots, videos) can help to attract comments and feedback without the commitment of actually downloading and playing the game, whilst also increasing the likelihood of piquing someone's interest enough to give it a go.
If your game has a particular theme you could also seek out non-gaming/development communities with an interest in the theme and politely (of course following any community rules) see if they're interested in giving your game a go.
Going into the real world can also be beneficial. Ask friends or family to give it a go -- maybe in exchange for a beer, some pizza, or whatever. Be cautious with the feedback you get from these sort of people though, as those close to you will often want to be encouraging and avoid hurting your feelings, and may not share their honest opinions; this is how terrible singers end up nationally televised on Idol or similar shows with no idea that they're not actually talented! As suggested in this recent article, make sure you're actually watching (or even recording, with permission) your playtesters, and learn from your observations rather than just what they actually tell you.
Expanding beyond friends and family, you could look for gaming clubs at local high schools or universities and see if they would be interested in giving a new game in development a try.
With mobile games, I've also had luck with "captive audiences" out in the real world. Go on a longer peak hour train ride with a couple of devices and a little sign saying "try my game" and you'll usually find enough bored commuters willing to give it a go that your devices will be in use for the whole trip. I once saw an article from a developer who tried something similar with the people waiting at the DMV. Obviously don't make a nuisance of yourself though! Obviously, this doesn't really work with desktop titles, unfortunately.
Overall, it's a tough problem to crack, and I don't think there are any magic solutions. There's not some magical community out there where every game will get all of the playtesting it needs or some magical formula for attracting people to actually give games a go.
Hope some of that helps! 
