iPhone or iPad lost or stolen? Here’s what you should do
 
If your iPhone or iPad has been lost or stolen, there are a lot of things you can do to protect the data on your device, and to try to find and retrieve it. Here are a few steps to help you out.
Check your iPhone’s location

If you had Find my iPhone enabled on your device, go to iCloud.com, click on Find My iPhone and you should see a map with all your iOS devices. Select the lost device, and keep tracking its location.

Turn on lost mode
To put your device in Lost Mode from the iCloud interface. Click on the dot representing your device on the map, and click on Lost Mode icon:

With Lost Mode, you can:

• Set a passcode, if you hadn’t already
  
• Display a custom message on the device, with your contact details and other info.
  

• If Locations Services were disabled on your device, enabling Lost Mode will automatically turn it on again.
  

Report the theft/loss to local authorities
You should also report the loss or theft of your device to local law enforcement. Law enforcement usually requires the IMEI number of your iPhone, which you can find on your device box. You can also find the serial number of all devices registered with your Apple ID from here.
Report the theft/loss to your carrier
If the iPhone is in offline mode, then to avoid your SIM from being used for malicious activity (the thief could put the SIM in a different phone), you could ask your carrier to suspend your line, and prevent unauthorised use. The downside to this is that you won’t be able to track the phone if it is turned on again.
Worst case: Erase your iPhone
iPhones and iPads tend to contain a lot of personal sensitive information like photos, bank account numbers, your email etc., so if you think you won’t get the device, you can wipe its storage clean. This will ensure that none of your personal information gets revealed. If you get your device, you can of course restore from an iTunes or iCloud backup. Note that if you wipe your device, you won’t be able to track it anymore, but the thief won’t be able to do much with the device either, as detailed in the next point.

Activation Lock
With iOS 7, Apple added a new anti-theft protection feature that ties your device with your Apple ID. So, if your phone gets stolen, the thief has to know your login credentials to turn off Find My iPhone or erase the phone to factory state.

As a precaution, you should keep a copy of your iPhone’s IMEI number somewhere handy, either in a paper note or in the cloud, so that even if you don’t have the iPhone box, you still have the number.