Lets say a girl knows your face, but you haven't really ever talked to her, but you have great reason to believe she likes you. You think she lives in your community since you saw her once and she saw you (or perhaps she was visiting family/friends), but for whatever reason you don't see her again. From then on, you try and look for her but no luck. As you are rummaging through Facebook, you find her profile.
Do you add her, even though she may not know your name (but recognizes your face), and ask her out, or do you just keep hoping you get another opportunity?