They'll do a search for you. Let me count the ways. You move and don't leave a forwarding address. You forget to give your new address to every institution holding money due you. Sometimes you don't know that money is due.
Some people die without leaving good records.
By state law, banks and other private companies, including nonprofits, generally can't hold unclaimed funds for more than five years. They're supposed to turn them over the state's unclaimed property office. The states list the missing owners in newspaper ads and on Web sites. They may also try to find you through telephone directories, credit bureaus and motor-vehicle records. Some states try harder than others.