Oh dear you know this exact thing happened to my friend who also liked a girl but could not confront that person so I then I came in the picture I told him to go ahead and tell that person directly that you like her and would want to know about her ,though he was a little uncomfortable in doing that but he listened to me and believe me coincidentally that girl even liked her but could not confess that and now they are married .So dear if you like this person just go ahead and confess instead of keeping that to yourself and hurting yourself more .Even if the person says no to you it does not matter what matters the most is that atleast you will cum to know the truth and face it rather that running away.
You should start to be friends with them (if you already aren't) and then if he/she likes you they would probably come up to you and ask you out. If you are the confident type, and will take both yes or no for an answer, go on up and ask them.
I'm in the situation and I am such a wimp I can't ask. :S
Just talk to him get to know him and then tell him how you feel. Good Luck!