I have a lot of contacts I've made over the years, and most of them I am not fb friends with.

I was thinking that having the Facebook app's contact finder search my phone and add people might be a good way to reconnect.

Would this come off as creepy? How could I sell it to the girl?

Well usually when the girl is interested you just wont fall out of contact. She will generally text you with some excuse, or just be like heyyy stranger!
If she doesnt text you ever again you probably have fallen out of her radar. But it might just be so that shes too shy to text you, and to know which case ypu are dealing with just text her with something that puts all the wheight of the conversation on her:
For example texting her just a "heyy" will have on one end of the spectrum a "heyyy i havent talked to you in ages! How are you??" Or she will ignore the text on the other side of the spectrum.
From that you can lead the conversation to adding her to facebook.

In conclusion if you add them right away yes it can be creepy if you havent talked to them in ages. But overall if you have not had success with this girls by now, i woulnt even botherwith them cuz once they say no to you in their heads, saying yes would mean lowering their standards. And good girls dont lower their standards.

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