how do i use gps to locate a missing phone

If you set up the Find My iPhone service prior to your iPhone going missing, then there is a chance that can be tracked, though it depends on a number of factors (the iPhone is turned on, connected to either the 3G or a WiFi network, or has not had the Find My iPhone service disabled or the iPhone been completely restored). Log into iCloud.com, or to MobileMe if you set the service up before iCloud was released, and go to the Find My iPhone section.

If you did not set up Find My iPhone, then there is no way to track it. Contact the police and change any passwords for any online accounts you may have used from your iPod (the iTunes Store, for instance).

Regards.