Tumblr has the single worst format for collaborative writing/RP out of every venue, IMO. In general they're also extremely focused on graphics and presentation and spamming gifs in every response, to the point where you may be passed over entirely if you haven't myspaced up your tumblr enough. You could have to deal with the SJW culture, and wanky fucks might target you and try to run you off if they don't like some insignificant aspect of how you play.

What the above anon said was also true of my experience. Psychotically clingy people OOC (one threatened suicide if I didn't stop playing with someone else who played the same character as them), most seemed to prefer talking about RP and our characters' dynamics more than actually playing it out, etc.