It's the worst when friends lose their phones, but now you can out your fellow Android-using brethren with the new version of Android Device Manager.
Any Android user can now log in as a guest to locate, lock, or remotely wipe their device. Once they've chosen the device's fate, they'll have to sign out to let you regain access to your phone or tablet. The user name isn't stored, either, so your friend won't have to worry about you having access to their device.
The update is slowly rolling out to Android devices everywhere. You can grab it now in the Google Play store.