Share 'Tumblr: A place for the twenties?'

I've been on Tumblr for a good 1 and a half months. Wonderful micro-blogging system, and I love the interface. Unfortunately it doesn't seem very "meet new people." I've been looking for other teenagers I can follow and make friends with. I only see 18-30 years old everywhere. I wanted to flip through public groups, but theirs no directory. Am I not looking hard enough, or is me and my 2 other f…