Facebook is now showing news articles in its search results and ranking them by how many "likes" and "shares" the articles have received from Facebook users. All Facebook says the number of friends who liked/shared an item also impacts the ranking. It's also worth mentioning that these result only show up in the dropdown below the search box. If you actually complete your search without choosing one of the items from the dropdown, the following search results page is a completely different experience with no news articles to be found.
There're currently two types of search engine results pages (SERPs): One is the drop down list of suggestions, a mix of Facebook content types (e.g. friends, likes, pages and groups). And, Extended search results page. Click 'see more results' and you'll get a full page of results which prioritize a 'posts by friends' section. Furthermore, in 'see more results' section you can drill deeper to 'posts by everyone'.
The ranking formula reads something like this: (Keyword relevance of shared content within your immediate friend network) divided by (ranked in order of who shared it) x (total number of likes)