First of all, learn the lesson: NEVER LEND MONEY TO ANYONE.
Then I would, for example, take his/her things and sell them. Watch, expensive shoes, TV, cellular phone, etc.
I mean, if you lend money to someone is because you think you know the person. So I would feel entitled to go to his/her home and grab whatever I think it would pay the debt. This part would be better be done if you go with a "big" friend of yours to watch over things (you don't want things to get out of control there).
