The recent study explored by Page Lever, which is an analytics tool for Facebook, proved that search engines are the utmost and significant traffic drivers for Facebook pages framing 34% of all external referral.

Google was the most important search engine transfer 27.57% of all outer traffic to pages.  These studies analyze 1000 pages, with a least of 10,000 fans each. Amazingly yahoo is sending more traffic to Facebook more than Bing (who joined up with Facebook).