From my experience, that is a very loaded phrase. If a girl is excited at the very prospect of being remembered by a guy, she likes him on some level. In any event, by so actively engaging with him, the girl has removed any creepiness from the situation. He is perfectly within the bounds of commonly understood contemporary social norms to ask her to hang out via Facebook. Of course, one never wants to ask someone on a date through any social networking application, but if the hang out goes well - there's his opening if he chooses to use it.
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