According to StatCounter’s GlobalStats research arm, Facebook generates 48% of all worldwide traffic from social media sites, followed by StumbleUpon (25%) and Twitter (10%). Facebook passed StumbleUpon in July 2009. Its share peaked in December of 2009 at 74%. In North America, however, StumbleUpon recaptured the lead in share of social media traffic with 40%, while Facebook dropped to 32% in March 2010.
Source: StatCounter Global Stats – Social Media Market Share
The data for March 2010 is said to be based on 13 billion page views across the global StatCounter network of member sites. The company only recently added social media services to its GlobalStats tool, and notes that its market share appears to fluctuate more than browser or search statistics.
The top social media sites to generate global website traffic after Facebook, StumbleUpon and Twitter are YouTube (6%), reddit (4%), Digg (2%) and MySpace (2%).
