When David Karp was 14, his parents recognized that Bronx Science could not keep up with him and introduced him to the animation producer Fred Siebert, with whom he interned. Mr. Karp moved on to work as the chief technology officer for UrbanBaby, an Internet forum for parents, and in February 2007, he founded his own company. It provided a platform for the rapid-fire posting of text, photos, quotes, links, music and videos. It was designed to make blogging and information-sharing easier. The program was called Tumblr, which, at the moment, employs 164 people and contains 96 million blogs and 44.3 billion posts. Mr. Karp, who was included in this year’s Forbes 30 under 30 list, has made a good sum of money—he purchased a condo in Williamsburg for $1.6 million last year, and his net worth is greater than $200 million—but he’s still figuring out how to monetize his website with meaningful modes of advertising. He dismisses the revenue models of Twitter and Facebook, with their “little blue links,” as he calls them. However Mr. Karp’s ambitions play out, the insignia on Tumblr’s About page keeps the company grounded: Made in NY.