Tumblr

tl;dr: Not recommended. May even be Considered Harmful.
The structure of the Tumblr platform has huge shortcomings when it comes to community discussion. "Reblogging" is a weak replacement for direct replies and is hard for other people to follow without special effort. Forget threaded and topically collocated conversation like in email or a message board or journal community.
It is frustrating to me as non-therian and non-fictionkin that those two things heavily dominate the "otherkin" population on Tumblr. I agree that therians can be considered a kind of otherkin in the broad sense of being non-human, and there is definitely community history of some folk moving in both circles, but it makes it hard to find the mythfolk, because therians (or "animalkin", since many of the folk on Tumblr seem to prefer the -kin terminology) have always been more populous overall than mythfolk (with the possible exception of dragons, although dragons are kind of a special case with their own history). Particularly, there seems to be little activity from elfae-spectrum folk, which I suppose mirrors the way we've become a small minority in the broadest-sense otherkin community we have today, instead of being a very common category in the narrower-sense otherkin community of the past.
I'm probably about the last fossil still hanging on of those of us from the days of mailing lists and/or boards and LiveJournal who tried out Tumblr in the early 2010s. Every other such person I used to follow has left. There's a big historical disconnect between ca. 1995-2010 vs. the Tumblr otherkin community of 2020+ which can be aggravating and even painful to see.
The #otherkin tag was OK (albeit often trolled or flamed by anti-kin) around 2011-2014 and then went downhill. Somewhere around 2016 or 2017 it fell over a line from "not great" to "may be anywhere from fluffy and useless to actively toxic, ugh, forget tracking this" and never recovered.
The #otherkind tag was a fair substitute for a while, since it was generally extremely low traffic (although you did still get some nonsense), but as of the first half of 2021 it's being taken over by fluff and crap as well, and I have to stop even semi-recommending it as an alternative.
Type-specific tags like #elfkin or #faekin may occasionally be OK, but don't hold your breath.
last updated: 8/19/2021