David Karp, Founder of Tumblr

So What Do You Do, David Karp, Founder of Tumblr?

Popularity, not profit, is the idea for this Web platform prodigy

When David Karp was 15, he dropped out of high school to be homeschooled on New York’s Upper West Side. At 17, he moved to Tokyo to work for UrbanBaby, an online parenting advice site with highly trafficked message boards full of urban-dwelling moms and dads. And when he was 20, he founded Tumblr, a…