Facebook visitors decreased in May, comScore reports

Facebook's US user numbers dwindled in May from April and March, according to data compiled by research firm comScore, in the latest sign that growth may be leveling off at the No. 1 social network.

Last month, Facebook attracted 158.01 million unique visitors in the United States, edging lower from 158.69 million in April and 158.93 million in March, comScore said. Keeping users coming back -- or combating fatigue -- is crucial for all social media services, analysts say. Facebook is consistently trotting our new features, including the "Timeline" interface rolled out this year, and more are expected with the deal to acquire popular photo-sharing app Instagram. ComScore has changed how it counts users, making year-ago comparisons harder. Under its old methods, comScore previously said Facebook had 157.22 million visitors in May 2011, which would make the new data a year-on-year increase of just 0.5 percent.