posts unwanted opinion on social media accounts here*
I mainly use my personal Twitter account, because I like how you can just tidbits of thought there that nobody will understand (heck, I think when I look back at those tidbits, I will have absolutely no idea what I was referring to). Posting consecutively doesn't feel annoying like it does on Facebook (which I barely use).
Ask.fm is no. Who's liking all these Selena Gomez and Pakalu Papito posts?? I will find you, and KILL YOU!
DCW's like this secret haven that my parents don't know about because they would kill me if they found out I still use this. :/
On the topic of fandoms, Tumblr might be the best place to go. It contains nice fanart of just about every fandom. However, I don't think you could have a coherent conversation about the work there. I'd go to a forum dedicated to this work (like DCW) or 4chan for that. 4chan has a bad rep, probably because of /b/ and the trolls there, but once you get used to on the rude atmosphere, you can get coherent conversation.
OMM: Heyy, Gravity Falls is returning!
OMM2: About to lose bragging rights
OMM3: @AL: username