6. Twitter

Originator(s): Jack Dorsey, Evan Williams, Biz Stone, and Noah Glass

Year: 2006

Worth: $8.4 billion (as of December 2011)

How it took off: Dorsey came up with an idea (after a day-long brainstorming session with the others on Twitter’s board) that had a person communicating with a group of friends using a single SMS. Williams, Glass, and Stone later came up with a name for the service, and the way it would work. Things really took off when people started using the 140 character limit to express themselves and to keep tabs on people they knew. From 2006 to 2011, Twitter has grown from a small social medium to a platform worth $8.5 billion, with more than 140 million users worldwide. Talk about explosive growth!

7. deviantArt

Originator(s): Angelo Sotira, Scott Jarkoff, and Matt Stephens

Year: 2000

Worth: $19 million (estimated, according to a report on entrepreneur.com)

How it took off: deviantArt, one of the biggest, longest-running social networks was created when its founders wanted “to build the deepest, most vertically integrated network that ever existed.” They’ve succeeded, and dA is the one online community for artists that has more than 14 million users, that aims at giving any artist (from the fields of art, literature, film-making, and photography)  a platform to exhibit and discuss his or her work.