Nothing makes website owners happier than loyal, repeat users, but it can often be difficult to find them. Now, a study by online ad network Chitika suggests that the two best sources may be Facebook and Digg.

The study, based on a sample of 33 million unique users across the Chitika publisher network in September, 2009, compared the number of visitors coming from major traffic sources – Digg, Facebook, Google, Yahoo!, Bing, and Twitter – to the number of times those visitors came back to the referred site. If a visitor came to the site four or more times over the course of a week, that visitor was considered a “loyal” user.

The results showed that Facebook was far and away the best provider of loyal users – over 20% of all visitors from Facebook visited the site four or more times per week. Digg came in second place with slightly over 16%.

Next came the search engines, Yahoo! leading the way with over 15% of referrals being loyal. Google and Bing were practically even at slightly below 12%, and Twitter came in last place overall with barely over 11%.

While Google naturally wins in sheer numbers, if a website owner can drive a thousand people to their site via Google, or they can drive the same number via Facebook, Facebook seems to be the way to go for creating a loyal reader.

Loyalty by Referring Site:
Facebook 20.69%
Digg 16.09%
Yahoo! 15.89%
Google 11.84%
Bing 11.74%
Twitter 11.08%

Source: 33,667,507 uniques across the Chitika network in September, 2009

For visuals and supporting data visit: http://chitika.com/research/2009/digg-facebook-loyal-readers