Help friends find their Android device with the Android Device Manager
If you haven't started using the Android Device Manager for your phones, we recommend that you do. But did you know that there's a guest mode you can use to help out other people? Just like how you would use the app. You can let a friend log in through guest mode to help them locate, lock, or wipe their device.
Source: Lifehacker | Download: Google Play Store (Free)