It's intentionally broken.

Despite many real (though also some exaggerated) counter-examples, Facebook does have features to protect privacy.

One of those things is you generally can't get very useful results from search unless you're friends with someone, or a friend of a friend (depending on the user's privacy settings). You can't see general trends, or even search for every person with a given first and last name in an area, for example.

It used to be more open, but they've heavily restricted the breadth of data returned from searches within the past few years.