Having already eclipsed MySpace in terms of worldwide traffic, Facebook is continuing to make gains in the US. The social network added nearly another million monthly visitors in September according to Nielsen Online, bringing its total to 39.9MM uniques. With MySpace’s traffic stagnant at 58.4MM uniques, Facebook is now more than 2/3rds the size of MySpace for the first time in the Nielsen report.

Stats elsewhere paint a similar picture. Compete has an even closer race: 54.9MM to 44.6MM, while Quantcast measures 66.8MM for MySpace and 45.2MM for Facebook. Here’s the comparative trend graph from Compete:







While we’ve known of this trend for a while, one interesting item to note: while Facebook continues to add visitors, MySpace isn’t really losing them – their traffic has hovered around 60MM uniques for most of this year. That implies that users aren’t necessarily leaving MySpace for Facebook, but rather, Facebook is reaching new demographics that MySpace was unsuccessful with previously – most likely, adults.

Nielsen Online’s full report for October is embedded below:



