New data from Experian Hitwise measuring traffic and engagement on social media sites highlights the rise of Facebook, and reveals a surprising decline in user engagement at Twitter.  ReadWriteWeb covers their findings for the top five sites.

The data shows the continued mercurial rise of Facebook.  As of September 2009, the number one social site saw an increase in traffic of 194 percent in year-over-year comparison.  The report shows nearly 60 percent of all social media traffic goes to Facebook.  Meanwhile the popularity of former star MySpace continues to tumble, with a 55 percent decline in traffic in the same period.

The growth category crown goes to Twitter, which had traffic skyrocket by 1,170 percent in the past year.  Yet even with that growth the data revealed a couple of surprises about the microblog site.  While making number four in the top five list, Twitter draws less than two percent of overall social media traffic.  It also had a precipitous drop in user engagement over the past year, which Experian Hitwise measured as falling from 36 minutes to 16 minutes per user.  Twitter is topped on the list by Tagged, a new social media player that has been cited for spamming and misrepresenting itself in emails to draw users.  The top five list is rounded out by myYearbook, another social site that the study shows might be past its glory days.

Check out the full traffic and engagement results for the five sites at ReadWriteWeb {link no longer active}.