This is probably not the place for me to go off on tangent, but why are you getting upset? Do you think he can finish this project on elance for $500 dollar? How is this going to affect you?
He is scummy guy. Ok. Agreed. But like eru said, you make your code available under MIT license. You can't have it both way of putting your code under a license like that and then complaining when someone uses it in a way you don't like. It seems very hypocritical to me to be angry if he is using your license properly. If I put $100 dollar out to charity and they don't use it in a way I see fit, that is my fault, not theirs.
Worst case scenario he makes someone to finish the app and makes a lot of money off it. And then you have a right to be angry if he violated your license in any way. But also you should think that you are very angry because you had app 90% of way done and someone gets all credit for taking it that last 10%. But then that is your fault for not taking it that last 10% yourself.
I will most likely lose all my 10 hn point for this but I would just drop a note to elance and then forget about this issue. Don't be vindictive about this. You are amazing person and have an amazing day, be more happy :) Good luck on being a doctor, forgot about this guy.