Report your lost or stolen device to local law enforcement. Law enforcement might request the serial number of your device. Find your serial number:
On the original box or receipt
On My Support Profile (supportprofile.apple.com) if you registered your device with your Apple ID
Erase your device. To prevent anyone else from accessing the data on your missing device, you can erase it remotely. When you erase your device, all of your information (including credit or debit cards for Apple Pay) will be deleted from the device, and you won't be able to find it using Find My iPhone. After you erase a device, you can't track it. If you remove the device from your account after you erase it, Activation Lock will be turned off. This allows another person to activate and use your device.
If you use Family Sharing, any family member can help locate another member’s missing device. Just have your family member sign in to iCloud with their Apple ID, and you can find any device associated with that Family Sharing account.