The best way to track an iPhone is to use the Apple approved application, Find My iPhone. This application works in tandem with the iCloud, and it shows exactly where an iPhone is on a map when activated.
Find My iPhone has a number of features that help track down a lost iPhone and protect it from harm. The Activation Lock feature allows users to lock an iPhone if it gets into the wrong hands. Through this feature, the iPhone can also be erased and reactivated by entering in an Apple ID and password.
Another feature of Find My iPhone is the ability to display a message to whoever finds or has the phone. For instance, if the phone is lost, the owner of the iPhone can put a message to the finder to call a certain number to report the iPhone has been found. The application also notifies the owner of actions done on the phone, such as when it goes into lost mode, a mode that can also be applied in the iCloud and Find My iPhone. When the phone is in lost mode, it can also be tracked, and a map displays where the phone has been over the past 24 hours.