Change your Apple ID password
If you use more than one Apple ID, you should change the password for each Apple ID that you have.
Change your password for other accounts
Change the passwords for other internet accounts on your device, like email accounts, Facebook, and Twitter.
Report your missing device to local law enforcement
Law enforcement might request the serial number of your device.
Contact your wireless carrier
If the missing device is an iPhone or an iPad with cellular, report your missing device to your wireless carrier. Ask the carrier to disable your account to prevent calls, texts, and data use. And if your device is covered under your wireless carrier plan, file a claim.
Remove your missing device from your list of trusted devices
Go to appleid.apple.com to remove the missing device from your list of trusted devices.