Hi B. R:
I am the mother of a son around the same age as yours, my son just turned 11 three weeks ago. I understand what you are going through but you have to start giving him the tools to take care of himself and to learn to make decision for himself.
You have to trust that you have given him the right tools to take care of himself and to make the right choices.
I have just recently allowed my son to adventure out on his own with his friends. But I have set up a perimeter in which he is allowed to travel. I bought a set of two way radios, not cell phone, so that he has to stay within that perimeter. We have been using the two-way radio for about 2 months and they have been working great. They have a 10 mile range and he can never use the excuse that he didn't have a signal.
No one knows your son as well as you do, trust that you have taught him well and he will do you proud.