The Web measurement firm found that Twitter sent nearly one in five visits to social networks and the same proportion to entertainment sites in February. Google ranked as the top visited after Twitter, followed by Facebook, Twitpic (a photo-sharing service for Twitter), MySpace and Twitter Search.

The top entertainment sites besides Twitpic were YouTube and Flickr. Other sites among the top 20 destinations from Twitter included Yahoo, MSN, Wikipedia and Gmail.

The data also showed that Twitter has more in common with social networks than search engines. "It appears that Twitter is being used as a social network and means of distributing content," wrote Heather Hopkins, a senior online analyst at Hitwise, on the company blog. "This is by no means the only way it is being used -- just one standout trend. Twitter.com's clickstream profile is much closer to a social network than to search engines or email services."

She pointed out that, unlike search engines, Twitter refers relatively little traffic to retail sites. (As more retailers tap Twitter as a marketing tool that could change over time.) And unlike email services, it drives less traffic to dating and business and finance sites.

Conversely, "a higher share of downstream visits from Twitter.com go to entertainment Web sites, in particular photo-sharing, and a much larger share go to blogs and personal Web sites (7.28% in February) and to news and media" sites, according to Hopkins.

The findings on traffic from Twitter underscore the growing role social media properties are playing in sending traffic to other sites. Hitwise recently released data showing that Facebook is now referring more traffic than Google to certain sites including PerezHilton.com, CafeMom, Evite and, highlighting a degree of reciprocity, Twitter.

And with the redesign of the Facebook home page and brand pages allowing more and faster content-sharing, referrals from the world's largest social network are only likely to increase. But to date, it looks like sectors outside Internet services and entertainment haven't seen much direct benefit from Twitter or Facebook.

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