Though not all phones are equipped with GPS locating devices immediately in their hard drives, many phones have advanced tracking devices and applications which users can install themselves. If you are trying to locate a missing person and the only information you have is a cell phone number, you may be able to use it, depending on the missing person's phone and its capabilities.
Report the missing person and the cell phone, number, and all of the information you may have on the phone and its capabilities to the police if the matter is serious and an emergency. The police department can often search for phone locations based on a GPS signal with more advanced equipment.
Find information on the type of phone the person who has gone missing has. If you already have this information, visit the phone's official website or the phone service provider's website to view more information on the cell phone. You can then view details on the phone's technology and if it has GPS capabilities enabled.
Determine if there had been any GPS applications installed onto the phone prior to the missing person's disappearance. This may help with finding the person even quicker. Browse the cell phone service's marketplace for GPS applications if you are sure the person who is missing had installed a GPS application. Alternatively, you can also call the phone company directly (or another person who handles the bill) to inquire about this information and downloaded applications if possible. Research phone bills for implications of downloaded GPS software to the phone. If you find information on an active GPS program, visit the company's official website. From here, you may be able to login or contact the company themselves to find more information regarding the missing person.
Review any "Location Based Services" the person may be a part of. Google Latitude, MapQuest, and Accutracking all keep track of users on their mobile phones from the services directly. Some social networking websites also have this enabled, so be sure to review these profiles as well for any indication of a location.