I have profiles on pretty much on all social media outlets, my main ones that I'm an actual person on are Twitter, Patreon, a little Tumblr, and a little FB, and all the other social media site mirror posts from these main places through "If This Then That" codes. (Super useful to automate like that)
I get the most out of Twitter. There's a really sweet awesome supportive webcomic community there and weekly comic chats that help us all get together and mingle.
Reddit has also been good for promoting weekly updates, but it's important to read each subreddit's guidelines before posting.
I've been getting more activity from followers on Facebook since trying out some of @michaelson's tips in his thread post here:
And since taking some friend's advice (through twitter lol) and treating my Tumblr page more like a blog and less link spamming, I've gotten better results there too. I post things like WIPs, tutorials, blogs about my art process, and the occasional Undertale fanasrt reblog lol
Each social media site has its own unique way of operating, so each one tends to require special attention. @_@ lol