We have all been a victim of this scenario. Go out, meet someone, get contact information, they say "Add me on Facebook" and leave. You do a search for them and find quite a few results (some with their profile pictures visible and others without). You initiate a filter by location, you still get a few results. So what's next?
It looks like a company started recently called Friendthem, a location based app which helps you find that person and send a friend request. You know those add-ons you get for Firefox or Chrome? Think of Friendthem as an add-on for Facebook. There is no need for a separate account, it just uses your existing Facebook account. You can choose the amount of information you would like to share. When you meet someone, you can instantly find out if you have any mutual connections and them then or later (it tags when/where you met said person). It's as simple as that. The app is available for Android as well as iOS phones. The video below will give you an idea of what they are all about: