If the amount of money is nondescript you don't announce the amount or the location, just that money was found. The police usually handle this aspect of the search. If it is a common bill, like a twenty (then) or maybe a hundred (now) you wait for someone to come seeking. If no one seeks it out then it may be an amount they didn't mind losing or perhaps the don't have the imagination to consider that the police may have it. At any rate you have taken reasonable steps to locate the owner. No more can be asked of you than that.