Tumblr is one of the most popular websites in the World, but most of its traffic does not come from search:
tumblr.com - SEMrush's main report for domain
It looks a little differently here:
Tumblr.com Traffic Statistics by SimilarWeb
One way or another, I was reading about it on the Net. They cut traffic to Tumblr, for some reason. It was because it was a competitor to Blogger, I think.
Other social websites that you can use are Pinterest, VK, Facebook, StumbleUpon, Sex.com, and Twitter, which is obviously very good. I know that there is automation tools for Pinterest, Facebook, and Twitter, and it is possible to add feed url to sex.com (they upload pictures from your websites there).