To trace who the owner of a cell phone number is, look up the phone number in the white pages or on websites, such as Sat-GPS-Locate or Mobile Phone Locate. You can also try to find the owner by entering the number in the search box on Facebook. Another way to identify the caller is to call them yourself and ask who you are talking to. You can also ask a friend to call the number from his phone.
To trace the location of a cell phone that belongs to a member of your family for free, download a GPS tracking application to the smartphone you want to track, and adjust the settings to allow you to track the phone. Some applications may let the owner of the phone know that it is being tracked, others don't because they are meant for use by parents. If the phone you need to track isn't a smartphone, go to the website of AccuTracking, and check if you can use this service on the particular phone model. However, this service is paid.
You can also track the location of your own cell phone in case it gets lost or stolen. There are many options available in the smartphone application store. Most of these applications allow users to track their phone from their computer. If you lost your phone and the app wasn't installed on it, you may still be able to locate it. Contact your phone's manufacturer for instructions.