If all of the above fails, you can use this scenario:
You start a normal conversation with them via instant messaging, phone, or in person. You explain to them that there is this person you like, but aren’t but you aren’t sure how will start up a conversation with them. You then ask how they approached their boyfriend/girlfriend. If they explain they don’t have one you are good, but if they actually answer they are taken.
Now depending on the answer you will be feeling differently and will want to express that. If they answer in the way that you want them to, you will be most likely overwhelmed with joy. If you don’t want them to have any ideas that you like them right away, just say, “Finally! Someone who knows how hard this is!” Or my best suggestion would be to ask right there.
If it is answer you are not looking for I can’t imagine you’d be feeling that chereful after hearing it, so if you sound kinda depresed and can’t hide it just let them tell their story and say “Oh… I dunno if that’ll work for me…. I’m just gonna have to think think this out.”
I hope you get the answer you want, and if you do, try to go for it.