8. 51.com

51.com

While many social networking sites strive to create global communities, others look to cater to very specific audiences. In the case of 51.com, the audience was a nation: China. In 2008, the site had 120 million members.

 

In other words: More than half of the 210 million Chinese citizens with Internet access at that time had a member account on 51.com. According to comScore, China has passed the United States in overall number of users on the Internet but the percentage of Chinese citizens with Internet access is still very low. In the U.S., nearly 73 percent of the population uses the Internet. In China it's closer to 22 percent.

Members of 51.com can create personalized profile pages, upload photos and write blog posts. The site has a reputation for pretty exceptional user engagement; most members visit the site multiple times each month.

The site plans to launch a major game project, with an investment of more than 100 million yuan (about $14.6 million U.S.) would only enhance this engagement. Investors in 51.com include Intel Capital, Sequoia Capital China and Redpoint Ventures, the company that invested in another well-known social networking success: MySpace.com.