
Facebook used to be just a place for friends to communicate, interact and share. But Facebook wasn't contented with that role, in the company with Ning, Tagged or Friendster. When searching for information, users typically leave the site and head towards popular search engines. Facebook wants to be the one-stop web utility and not just a social media hangout. Not long ago it revised its page layout to emphasize use of search engines. Unlike its early days, Facebook now displays people's profiles, groups, pages and web results. Therefore its usefulness extend beyond simple searches; it becomes a legitimate search engine more than just an internal site search feature.
As we consider Facebook's 400 million plus users spending longer hours to play virtual games, viewing photos or writing on "walls", chances are, a portion of them should be using Facebook search at any given time. If our Facebook fan page does not appear on the autofill results screen, we are missing out on Facebook's opportunity. Heck, many sites don't even have Facebook pages.
But to those who wish to rank for Facebook pages, being there as the user types the first few letters of a search query brings lots of opportunity (brand exposure, to begin with). However, unlike typical search engines where rankings are based on finite set of factors, Facebook relies on user behavior (past visitors, likes, events, clicks, connections, etc) so that the search form can be more appropriately called suggest form rather than search form.
Possibly, Facebook does this auto suggest feature to attract users into clicking them and staying in the website instead of going directly to the search results page -- a portion of which is served by Bing -- whose quality is still inferior compared to Google's.
According to Aim Clear Blog, Facebook Suggest ranking factors could be the following: