I've been using tumblr for nine years... I guess since it opened. It was great in it's hey day but it's dying down now. All the blogs I used to follow have just dropped. Part of it were people I knew IRL that I now keep in contact elsewhere, another part was the lolita community which I fell out of (and I think maybe they moved too?), and the rest IDK. I was using it lately to post GIFS on my gif blog since tumblr is really the only place for the sentai/toku fandom to share gifs.
I'm not sure who's using tumblr anymore. They scared away all the artist and they mostly focus on instagram, and the really ambitious ones that wanna make money go on youtube. All the young/kids who are into fandom are on amino. Even the SJW moved over to twitter.
but here ya go: