Fortunately the manufacturers have programs that will help but you have to take the time to install them. Apple has I cloud and Android phones have Android device manager. Both require that you have location services enabled on the phone and both have some powerful tools if you have your phone lost or stolen.
You can go to the appropriate website to see all of your contacts and data.
Assuming the phone is on: You can see, on a map, where it is, you can put a password on the phone, you can make the phone ring or you can erase all of the data on the phone.
An additional service I recommend is Carbonite. http://goo.gl/cg7sQ3 This is free for your phone, has all of the location services of the other programs and will also backup unlimited amounts of pictures.
No mater what you choose you should still have basic security on your phone. A 4 digit password will, at least, keep the regular people out. These passwords can be broken but require special software.
Of course the best action is to never loose your phone or let it get stolen. Let's hope for the best but plan for the worst.