Reddit communities are good, join a small one if you want to engage with people and make friends but joining the big one's are a good way to join into a discussion although I do find reddit really toxic at times. Google+ is also another one, join a community that is relevant to your channel and again start posting/engaging on there. It's not as nice as YTtalk but I'd suggest again joining smaller one's since I got a few people who follow me on there. And the last one would be YouTube itself, check out people's content who are as small as you and leave feedback in the comments section or get engaging with them. This is a good way to grow and I don't mean spam obviously don't ask people to subscribe or do sub 4 sub but if you find a genuine person and engage with them in the comments they are more likely to check your channel out. Watched a guy do YouTube for two months and just engage with people in the comments, he grew to 500 subs during that time because he knew how to use social media and engage in those platforms the right way.