He likes you and doesn't know how to proceed. If you like him and want his attention do what all woman do, through out the bait and let him bite.
Be friendly sit by him over coffee, chat him up so he thinks he is chatting you up. Let him know what sort of things you like to do for leisure, "Oh I really like the movies, I'm looking forward to seeing *** *****". Yes pretty blatant but guys don't always think very well, particularly when woman are in the equation.
I'd be very careful of play-fighting BTW, it isn't very lady like (sorry

) but can cause conflict among males who may regard 'fighting' of any sort as territorial stuff. If he started to get jealous then it can lead to problems for him later.
I also agree with Cindi, work relationships are usually a disaster.
Enjoy
Cindy