Lost cell phones usually get turned into the store manager or to the police. Others try to contact people on the contact list to let them know they have the phone. Here are steps on how to find a stolen or lost phone.
Call the number of the phone. If the person who has the phone answers it, explain to them that you know the phone was stolen and that you know their name and address and will report them to the police if the cell phone is not returned. (Do this even if you do not know the crook's name and address).
Hire a private detective to help you find your stolen cell phone. There are people who have skills and techniques for finding lost or stolen cell phones.