[qi:109] Facebook accounted for nearly 60 percent of all U.S. visits to a social network in September, nearly tripling over the same month last year, according to the latest stats from web traffic intelligence company Hitwise. By comparison, MySpace (s nws), which took the No. 2 slot, saw U.S. visits to the site plunge to 30.3 percent from 66.8 percent in September of 2008. Meanwhile Twitter’s percentage of visitors mushroomed to 1.84 percent last month from .15 percent in the same period the year before — a surge of 1170 percent.
With Twitter’s booming growth, how secure is Facebook in holding its top spot? These results indicate that the social network space is more sensitive to new entrants relative to the search engine market, where Google (s goog) has long held the majority share even in the face of Microsoft’s (s msft) effort to take some of it away with Bing. Though Facebook’s worldwide audience now tops 300 million people, it only overtook MySpace in terms of the number of unique U.S. visitors back in May. Twitter eclipsed MySpace in the UK last month. While Facebook won’t be dethroned anytime soon, how long will it be before Twitter starts chomping on its heels? A lot of it will come down to whether MySpace CEO Own Van Natta’s strategies lure people back to the struggling social network.