... Says the woman who voluntarily consumed Rophenol. :P
Repeatedly sneak into his apartment and steal his meth. Feed his delusions that a convenient and obvious suspect is "after his stash" - hopefully to the point of misdirecting his easily manipulated suspicions, so as to divert his attention, and thereby stealthily gain access to his shit. Flush it. (Important caveat: if he keeps all his stash on him at all times, this may not work.)
Convincing him that a given, convenient "target" is responsible for the theft should be easy in light of the meth addict's notorious disassociation from reality, and propensity for delusion. A fellow user might prove your best potential target.
Step one is to get him to stop dealing, that will fuel his habit indefinitely and he will associate with people who do it all the time.
Do this by, calling the cops or flushing the stash.
Step two is getting a replacement drug from somewhere, by this I do not mean coke or anything like that. I mean the ones doctors use to help people deal with withdrawal.
Then finally keep on off it by limiting his contact and by forcing him to be in social circles where it is not permissible.
Figure out what drove them towards escapism. There is a point in time where they gave up on themselves. So figure out what that was, and then figure out a way to get them to believe in themselves again.
Might have to remove stigmas which are difficult to remove due to societal perceptions. Example.
"My son died, it was my fault for not being there, so now I am going to smoke meth and drink myself stupid as a form of escape and self-punishment."
So, good luck with that.
"Giving up" might be wrong terminology. They could in fact simply be taking on too much weight, burden or guilt.
I've heard of people using stay's approach to help people break an addiction. Idk if it works with meth, tho. That's some nasty shit.
You might have to take Cain's advice and cut him/her loose. Most addicts will sell their own grandmother for their next hit. If you value your possessions, you'd be wise to stay away from them.
It sucks when the addict used to be a close friend. Maybe find a way to cut him/her loose till s/he can clean up on his/her own and look up your old friend in 10 years or so. My experience with these things has demonstrated that 10 years down the road, these people are usually on the same street corner doing the same old tired thing, but with fewer teeth and a lot more scars and saggy skin.
Better them than me. It's all I can do to help myself, without taking on the burdens of people who refuse to help themselves.
You never know, tho. I've seen people turn their lives right around in that amount of time. The ones who do are the kind of friends you'll want to grow old with. They always have the best stories to tell :)
Best just begin to dig his grave, once hooked it is highly unlikely for him to come clean. Unless he or you has the cash for a rehab program which is big bucks. He most likely won't come clean. I've watched multiple friends and even more acquaintances die from either meth or heroin. Lots of guys speedball which is taking both meth and heroin at the same time. For literally the best feeling in the world.