I am Samuel and I am going to help.
Do you know his google id and password?
The only self help options are tracking with a google account (which you need his log in information or a preloaded tracking app which I assume you did not install given the fact you a seeking help in this area. You will have to give his information to the authorities as the can use 911 tracking or request text transcripts from the carrier themselves. You can not do these things unfortunately with out a subpoena.
I am very very sorry to hear about your son.