Social networking sites are feeding off each other's good will, according to a new report by competitive intelligence service company Hitwise.

Facebook's traffic has doubled in just over 18 months, but MySpace still receives most of the Web's social networking traffic. MySpace captured 79.7% of social networking traffic in April, according to figures released by Hitwise on Monday. Facebook accounted for 11.47% of social networking visits, while MySpace alterative Bebo drew 1.28% of the traffic last month, according to the Hitwise report.

MySpace visits rose 70% from April 2006 to April 2007, while the percentage increase for the lesser-used sites was much more dramatic, according to Hitwise. Facebook visits increased 126% from April 2006 and Bebo's traffic rose 184% from last year, Hitwise announced.

Facebook opened its site to users without school affiliations in September and has experienced a 106% increase in market share since then, Hitwise reported.

"Opening up to the entire Internet audience had a positive effect for Facebook," LeeAnn Prescott, director of research at Hitwise, said in a prepared statement.

Hitwise also found that social networking sites drive traffic to each other. Nearly 25% of upstream clicks to 19 top social networking sites originated on the dominant MySpace last month. Nearly 3% of upstream traffic to 19 top social networking sites originated on Facebook.

"Clickstream data indicate that users at other social networking sites may be experimenting with Facebook as an alternative site, which may help it attain critical mass among non-collegiate users," Prescott said.

Online community Imeem and BlackPlanet.com rounded out the top five social networking sites to capture traffic in April, according to Hitwise. Tagged, Yahoo 360, Xanga, Hi5, and Gaia Online rounded out the top 10.