1.2 billion users worldwide -- 82 percent of the world’s internet population over the age of 15 -- now log on to a social networking site.Facebook, the third largest web property online, is king of all social networking sites. Visits to Facebook accounted for one in every seven minutes internet users spent online in October and 75 percent of all time spent on all social networking sites.

Twitter is the top dog when it comes to microblogging but China’s Sina Weibo is growing quickly too. Sina Weibo grew 181 percent over the last year and was the tenth largest social network in October; Twitter grew 59 percent during the same period.

 Social networking is not just limited to the web. Close to 65 percent of all smartphone users in the US visited a social networking site in October; two in five used their mobile device to connect to a social network nearly every day.

Internet users in Israel were the most engaged social networkers in the world, racking up an average of 11.1 hours per visitor on networking sites in October -- close to double the worldwide average of 5.7 hours per visitor.

Latin American countries accounted for five out of the top ten most engaged social networking countries while the United States, surprisingly, didn’t even make it into the top ten.

Top ten most engaged countries for social networking in October 2011, with average number of hours per visitor:

Israel - 11.1 hours
Argentina - 10.7 hours
Russia - 10.4 hours
Turkey - 10.2 hours
Chile - 9.8 hours
The Philippines - 8.7 hours
Colombia - 8.5 hours
Peru - 8.3 hours
Venezuela - 7.9 hours
Canada - 7.7 hours

                                                     [Source]