Praise be to Allah.
He has to make announcements about it in the places where people gather in the cities or towns at either end of the route where he found the money, and elsewhere (for example, he can put announcements in gas stations and police stations along the route), and wherever he thinks the owner may live. If a year goes by without him finding the owner, the money becomes his and he can keep it until he finds the owner, or he can give it in charity on his behalf. If he finds the owner after that, he should tell him what he did. If the owner accepts that he gave it in charity, that is fine, but if he objects then the finder should compensate him, and then he (the finder) will have the reward for giving charity. Or the finder can keep it with the rest of his money and give it back to the owner when he finds him.