Pinterest, a two-year-old social bookmarking site that lets users collect and share things they like on the web, is driving increasingly significant amounts of traffic to retailers' websites.

The service enables users to create online bulletin boards, or "pinboards," for popular categories such as home decor, food and wedding inspiration. Members can use Pinterest's "Pin It" bookmarklet tool and iPhone app to save things they see online and offline, and explore and repin the images their friends collect via their personal newsfeeds. The website is especially popular among women, who account for 58% of Pinterest's traffic, according to Experian Hitwise.

The site's popularity is quickly growing. Pinterest's traffic increased more than fourfold between September 2011 and December 2011, bringing in 7.51 million unique visitors in December alone, data from Compete indicates. The amount of traffic Pinterest sent elsewhere has risen accordingly, becoming a top five referrer for several apparel retailers, according to internal data from Monetate, which provided the infographic below.

Although Pinterest is becoming a significant source of traffic for retailers, search still dominates, and the site has yet to prove itself as a potential sales channel. At present, scant data is available about the social network's conversion rates.

[via Monetate]