I have a personal twitter and a twitter specifically for my comic! I find Twitter is a really good place to network with other creators who are interested in comics, and it's probably the social media I feel most comfortable in. My personal twitter is the one that interacts with people and advertises my comic and posts art and talks about life and is pretty chill and casual -- my comic's twitter is a backup for people who want to get updates about my comic on twitter, but aren't interested in my personal tweets and just wanna use it like an RSS.
I also have a personal tumblr and a tumblr specifically for my comic -- these I consider a little more disconnected, since my personal tumblr doesn't post most of my comic updates, and I wanted people to be able to follow both! They do reblog each other occasionally though, and my personal tumblr still posts things that relate to my comic a BUNCH.
I like tumblr a lot! My personal tumblr is the place I have the largest following (~2k), it's another place where I feel like I have the freedom to be silly and casual, and it's the place where I feel I get the most response to my work, even non-fandom stuff -- BUT there are definitely a few fandoms I've participated in, and a big percentage of my following first came from that. On tumblr it's harder to do well by being mostly promotional, and it works a lot better to join in with other communities in addition to posting your work.
Twitter and tumblr, to me, feels like the difference between a like... business convention and a party. Both are good places to find people who might be interested in your work, but at a business convention you network with other professionals, pass out your business card, etc. At a party, if you go around passing out business cards and promoting yourself, people aren't gonna want to hang with you; you're gonna make more contacts by finding some people talking about last night's [show you like] and joining in.
I do have a facebook for my comic but I don't find a lot of response there. My problem with Facebook is that, unlike Twitter and Tumblr, I'm not expected to post multiple update reminders... but, it specifically keeps my post from reaching everyone who's liked my page. If I post an update, it'll show up on some follower's timelines, and if those followers don't engage with that update post in any way, Facebook won't show the post to other people who've liked the Runewriters page. That just kinda irks me on principle.