Breakout Companies of 2010

J. Dong/Flickr
5 of 11

San Francisco
Founded in 2004

Why they’re on the list: For adding 12 million new users

Social media was once simply a set of tools entrepreneurs could use to promote their businesses. Now, with the advent of Yelp, customers can share their feelings about their latest shopping experience in a whole new way. The company, which is based in San Francisco, provides a forum where some 38 million unique users a month post reviews and ratings of businesses. With more than 12 million reviews now available, the site has become a go-to resource for users to evaluate the merits of thousands of restaurants, hotels and service providers in their neighborhood. What has helped the company reach a new level, though, is the launch of Yelp’s iPhone application which has been responsible for generating about one call every five seconds to a business.