I would step on the money first and look around to see if someone is looking. Then I'll pick it up.
That's the most reasonable thing to do. Because the personal who might have lost it would have been long gone. Asking anyone else around just wouldn't be of any use.
Having said that, me and my friend lost our carry bag once in Dubai on a bench. It had our money and passports. We remembered a little while later and went running back to the bench.
There were too men sitting there with the bag looking for the person who lost their bag. We showed them some proof that it in reality was out bag and thanked them.
But that was a bag, not plain old money. So there's a difference.
My response on mylot.com on a similar topic