Before you can locate your devices, you need to set up iCloud and turn on Find My iPhone on each of your iOS devices and Mac computers. Find My iPhone requires an iOS device or Mac that meets minimum system requirements.
Important: To see all your devices in Find My iPhone, use the same Apple ID to set up iCloud on each of your devices.
Set up an iOS device
On your device’s Home screen, tap Settings, then tap iCloud.If you’re asked to sign in, enter your Apple ID or, if you don’t have one, tap Get a Free Apple ID, then follow the instructions.
If Find My iPhone (or Find My iPad or Find My iPod) is turned off, tap to turn it on.
Tip: For added security, set up a passcode that needs to be entered before anyone can access the apps and information on your device. To set up a passcode, go to Settings > Passcode or Touch ID & Passcode. If your device has iOS 5 or iOS 6, go to Settings > General > Passcode Lock.