That explains why he's refusing to tell you where he's going/been. To your son, it's perfectly reasonable and logical to not tell you - because its easier for him to face your wrath for secrecy than your wrath of "what you doing at so-and-so's house". He gets your wrath either way, just lesser of two evils.
The way youth workers tackle this is to build a trusting and respectful relationship. Then try to educate teens out of drug use and peer pressure. Rather than authoritarian approaches. That said, aspects you can and do control need strict boundaries - like your behaviour in your home, treatment of family members etc. But to assert those boundaries he needs to have some respect for you and care about your opinions.
If he doesn't like you, knows you don't like him, it's going to be difficult to get him to respect you enough to do things you ask. As they get older "because I said so" often doesn't cut it. Personally, I'd work on bonding with him, building a relationship and trust.
A good way to start might be life360 - I'll not pass comment on where you are as long as you have it on so I know you're safe. Then stick to your word. So it means your side of the agreement is not having a go at him when he's said his mates.
Then build some rules around weed - for example it can never be in your house and explain why (educational moment) - the legal side, safety around children, animals etc, social aspects (smell when guests here), moral aspects. Don't lecture - just depart facts.
Also - make an effort to take an interest in his changing lifestyle - what's he into? Who are his new mates? Would they come to your house? Offer a trip out with new mate(s), or pizza and chill night with them, teen only BBQ, take to football match, or whatever he's into. I'm aware some of those sound twee, but he will be into something, so engage him in it and embrace (metaphorically) this new mate instead of demonising him. He might be a decent boy just like yours.
With the weed - bottom line is, if he wants to do it you won't stop him. He will likely experiment and grow out of it. Don't let this battle destroy your relationship with your son - because that could be the spiral that keeps him smoking and worse. Instead use a positive relationship to keep chipping away and reminding him all the negatives so he can eventually make his own choice to stop.