http://www.semrush.com/info/tumblr.com?db=us
They've become not very popular with Google a while ago, but it may be changing now. There is articles about it on the Net. They are still popular, as they are getting people from other sources, I think it has been mostly other social media sites. I have not been using it for a while, so I am not sure exactly which. There is some info on
http://SimilarWeb.com too.