While 2008 was Twitter’s hockey-stick year, Twitter’s little brother FriendFeed is also beginning to show hockey-stick tendencies in its growth. According to comScore, FriendFeed attracted 950,000 unique visitors worldwide in December. That’s a tenfold increase since June, when comScore counted only 93,000 unique visitors worldwide (and nearly double since September, when it was 550,000).

Twitter.com, by comparison, which is raising money at a $250 million valuation, has four times as many visitors (4.35 million worldwide in December). While recently there was some debate about whether Twitter has passed Digg, the real question might be whether FriendFeed can ever catch up to Twitter.

At the very least, these numbers suggest that FriendFeed has global appeal. ComScore counts only 172,000 unique U.S. visitors in December.

Update: Two counterarguments.

1. A large percentage of the content on FriendFeed are merely repostings from Twitter (see comments). So you could argue, and many do, that FriendFeed is simply riding on the coattails of Twitter and will never actually catch up.

2. This comScore data merely measures unique visitors and does not necessarily correlate with the number of users on FriendFeed. If FriendFeed gets a lot of its traffic from Google and other search engines, for instance, then those visitors would not necessarily be registered users (although they might become users once they discover the site).