If the kid suspects he is being tracked, all he has to do is turn off his phone and borrow his friends' phones when he's where he shouldn't be doing what he shouldn't do.
I think even Family Locator would be foiled by simply turning off the phone.
I really would recommend Mobil Spy. Your kid *will* know it's there, and maybe that will have the sunshine affect that you need. By knowing he is being monitored, he'll clean up his act. And Lojack the car, too

I'm sure he won't think you're doing both.
While a spy app may verify your suspicions, what would you do with that info? Knowing the answer is sometimes irrelevant to the solution, because it just clouds the real problem. I can imagine you confronting him, "You said you were at X but you were actually at Y. Why did you lie to me?" -- He can say, "Yeah, so I did." Then what would you do?
Whatever "that" you come up with can be done without the spygear, you know what I mean? And you will have to do it regardless if he's telling the truth or telling a lie to fix what's wrong.
Please, please, don't read this as judging. I'm just offering an "app-less" way to think about solving the problem.
Technolgoy can be bypassed by turning off the phone. Well-chosen words and actions will have lasting impact, but perhaps not immediately.
You sound so at the end of your rope and I am so saddened and touched by the extent of your love for your son. He's lucky to have you as his dad. Someday he will acknowledge that, probably just not now.
I wish you the very best of luck.