Arabian man snatched away my money

I just came out from the UOB bank after withdrawn some cash. There was this well dressed Arabian man came down from a car showing me his US100 dollars for fast exchange. While I pull out my wallet and looking for the $, out of sudden he snatch away all my cash and pretending the $ was his and start to walk back to his car steadily. I was stunt and don't know how to react, so I try to go after him but he just ignored me like I am a sales person who keep bothering him. In his car, got a woman and two kids.

If I scream, do you think people will believe what I said? :( I should have scream and make a big FUSS.....