Here's the details, according to a recent report released last week by Experian Hitwise: Facebook accounted for nearly six in 10 US visits to social networking websites in September, making it the uncontested leader among the custom category of 155 networks that Experian Hitwise tracks. US visits to Facebook increased 194 percent from September 2008 to September 2009.

MySpace, which was far and away the most popular social network a year ago, received the second-highest market share of US visits in September with 30 percent. Visitors to MySpace declined 55 percent from a year earlier.
Twitter had the largest percentage gain in market share of visits among the top five visited websites, increasing 1170 percent from September 2008.
US visits to social networking websites increased 62 percent in September 2009 compared with September 2008 among Hitwise's custom category of 155 social networking sites.
MySpace Is Stickiest
MySpace had the highest average time spent among the top five most visited social networking websites, with 25 minutes and 56 seconds--a decrease of 12 percent compared with September 2008.

Facebook recorded the most growth in average time spent among the top five sites, increasing 23 percent year over year, to 23 minutes in Sept.
Overall time spent on social networking websites decreased 20 percent in September 2009 from September 2008.
User Base Gets Older
Looking at the demographic breakdown of visitors to MySpace and Facebook, users 18-34 years of age still lead, as 32.27 percent and 26.96 percent of US visits, respectively, came from those combined age groups in September 2009.

Those numbers represent a 13 percent decline for MySpace and a 10 percent increase for Facebook in year-over-year growth.
For Facebook, the number of visitors who are 55 and older increased 108 percent in September from a year earlier, while visitors from that age group to MySpace increased 26 percent.
Overall US visits to social networking websites from users who are 55 and older have increased 77 percent year over year. Visits from users 18-24 have decreased 33 percent year over year.
Ann Handley is an 11-year veteran of creating and managing digital content to build relationships for organizations and individuals. Currently, Ann is the Chief Content Officer of http://www.marketingprofs.com which provides strategic and tactical marketing know-how for marketing and business professionals through a full range of online media and live events. She also blogs at http://www.annhandley.com, her acclaimed personal web log.
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