NEW YORK — In less than eight months, Facebook has doubled its user base by signing up another 100 million people from around the world, officially hitting 200 million last week.

Its population is now higher than Brazil's and Japan's.

The ubiquitous online hangout, available only to college students when it opened in 2004, has been growing rapidly since opening up to everyone.

But how long can that continue?

After a meteoric rise, News Corp.-owned MySpace has petered off and now has roughly 130 million active users, according to comScore Inc. Facebook could ultimately plateau as well. After all, while more than a billion people are connected to the Internet, that doesn't mean they all want to be on Facebook.

Still, even if it's inevitable that Facebook's growth will slow down at some point as the site runs out of prospects to convert, Facebook continues to change what it has to offer, meaning today's holdouts might decide later to join after all.

"What's striking to me is how Facebook has become a kind of dashboard for Internet users," said Lee Rainie, director of the Pew Internet and American Life Project.

He said Facebook, along with MySpace and other social sites like Orkut from Google Inc. or Bebo from Time Warner Inc.'s AOL, have clearly changed the online experience for many people.

Facebook's expansion has been peppered by growing pains, from concerns about how it handles users' private information to site redesigns that irked tens of thousands of members.

And just last week, the company announced that finance chief Gideon Yu will be leaving, as Facebook looks for a replacement with "public company experience." Yu had worked at Yahoo Inc. as treasurer.

On Wednesday, Palo Alto, Calif.-based Facebook also updated its display of site statistics.

According to these, more than half of its users log in to the site at least once a day, and the fastest-growing demographic is people over 35. About 70 percent of Facebook users are outside the United States (MySpace still claims to be the nation's largest social network).

For those itching to know if they are popular enough: the average user has 120 "friends" on the site.