13. Ori Allon and Robert Reffkin

Cofounders, Urban Compass

Ori Allon and Robert Reffkin's startup Urban Compass helps people find places to live in New York — and it’s worth about $360 million, after a $40 million round of investing in July.

Allon's first company sold to Google and his second company sold to Twitter. UrbanCompass is already worth more than both of those startups combined.