Pinterest

Pinterest is now the fastest growing site for referral traffic, according to a new study by content-sharing company Shareaholic. If Google+, YouTube, and LinkedIn's referral traffic were added up, they still wouldn't drive as many users as Pinterest.

The premise behind Pinterest is for users to gather, organize, and share things they find on the Web, such as home decorations, clothing, and food. The end result is curated pinboards that are meant to help friends discover new items or get inspiration. Currently, Pinterest is invite-only.

In the study, Shareaholic aggregated data from more than 200,000 publishers that reach 260 million unique monthly visitors. It found that Pinterest grew from 2.5 percent of referral traffic in December to 3.6 percent of the referrals in January.

Just six months ago, Pinterest had only 0.17 percent of the referral traffic. Now it's leagues ahead of Google+, MySpace, Reddit, YouTube, and LinkedIn, which is something for a site that's still invite-only. In fact, it's practically tied with Twitter and Google, which have 3.61 percent and 3.62 percent respectively.

The top traffic driver continues to be Facebook with 26.4 percent and far behind is StumbleUpon with 5.07 percent.

In December, Pinterest received 4,000 percent more visitors than it had six months earlier, which deemed it the "Number 10" social-networking site, according to Experian Hitwise. However, in the finicky world of social networks, it's unclear what will happen when Pinterest moves beyond its invite-only phase.