The best source of traffic is Facebook. The social networking site’s users are the most loyal referred visitors, according to an analysis of 33 million September internet users by the ad network Chitika. More than twenty percent of Facebook users loyal are loyal visitors. For the purpose of the study, users were considered loyal if they visited a referred site four or more times per week. Digg and Yahoo! were second to Facebook, with 16 percent of each site’s users considered loyal.

While Facebook and Digg have the most valuable visitors, search still dominates volume, which is obviously one of the conundrums content providers face today.

According to a related study Chitiki published in September, search still rules referral to a tune of 97.82 percent.

Only five of the top fifty referring sites are social networks, led by StumbleUpon, by far the most successful social media referrer, was responsible for 0.27 percent of referrals. Facebook was 17th with a share of 0.06.

Interestingly, Twitter referrals have fallen dramatically, or, as Chitika puts it, “Twitter users appear to be becoming link-blind.” The microblogging service has fallen from 24th on the list to 44th, its referrals dropping from 0.05 percent to 0.02 percent of total referrals.

Social networks were second to search, but represented only 0.55 percent of the referrals overall. Editorial followed closely, accounting for 0.47 percent of all referrals.

“In all, it would appear that while social media is increasing in its ability to generate outbound traffic, those increases are not at the expense of search engines, which continue to increase their referral dominance,” according to Chitika’s press release.

UPDATE [4:57 p.m. PST]: Nielsen just published a similar study, but focused on discovery. Eighteen percent of users see social media as "the core to finding new information," while 37 percent rely on search as their primary tool, 34 percent for portals and 11 percent for specialty sites like or CNET.

By Mark Alvarez