Field tested this one the other day and it worked like a charm for me. Walk up to a girl and open with, "Let me get your opinion on something. This past week three people have come up to me and told me I look just like (insert famous celebrity). Do you see a resemblance?"
May it was just becuase I do look strikingly like Michael Phelps, but it really got the conversation rolling along.
Good follow up would be to ask them if Lifetime was doing a made for tv movie on their life and they had to cast one actress to play them who would it be. Regardless of what they say, neg them by either putting down the celebrity they picked for themselves or casting someone else that would make them feel semi-offended.