How can I contact the owner of a lost iphone?

Turn it in to the lost and found where you found it or turn it in to the police. There is no way for you to find out who lost it.

The right thing to do is to turn it over to the police.

Apple will not become involved with locating a phone owner.

Thank you for at least trying to do the right thing! The advice you've been provided is about all you can do.