Moreover if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother. 16 But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established.
17 And if he shall neglect to hear them, tell it unto the church: but if he neglect to hear the church, let him be unto thee as an heathen man and a publican.
18 Verily I say unto you, Whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven.
19 Again I say unto you, That if two of you shall agree on earth as touching any thing that they shall ask, it shall be done for them of my Father which is in heaven.
20 For where two or three are gathered together in my name, there am I in the midst of them. -Matthew 18:15-20
I'm not sure if that this verse would refer to that, or not. However it still seems like the best approach. Obviously be gentle with how you approach the situation.
But sanctify the Lord God in your hearts: and be ready always to give an answer to every man that asketh you a reason of the hope that is in you with meekness and fear -Peter 3:15
Pray that god puts conviction on him for his actions? Especially since he's taking an active role in leading those in church.
The saying is trustworthy: If anyone aspires to the office of overseer, he desires a noble task. Therefore an overseer must be above reproach, the husband of one wife, sober-minded, self-controlled, respectable, hospitable, able to teach, not a drunkard, not violent but gentle, not quarrelsome, not a lover of money. He must manage his own household well, with all dignity keeping his children submissive, for if someone does not know how to manage his own household, how will he care for God's church? -Timothy 3:1-7
I cannot post links, but google "what the bible says about church leaders". I use openbible for most of my questions. He might come up with the statement "I don't do it while at church." Well obviously not, but still if he wants to take such an active role in the church he needs to give it up. Either that, or step down from his role, and continue to do as he pleases.
I smoked pot before I came to god. A few years ago is when I turned away. I was reading the bible after smoking, before I went off to play a videogame. I could not concentrate on the bible that well (obviously stupid to smoke, and read, but I was smoking preparing to play video games just happened to read the bible I guess.) I felt that I needed to give up pot, and follow the bible, and god, or continue to smoke and do as I pleased. Unfortunately I did as I pleased, and pretty much left god out of my life. Thinking about it makes me very sad, but alas I guess that's what had to happen. Everything happens for a reason. At least I believe that. God does work in mysterious ways.
However you handle the situation handle it with care. I believe it better to do it with love, compassion, and patience rather than the opposite. Take the time to think it out, and pray on it. Don't rush into the situation, like I just said. Give lots of thought about it, pray for it, and look into it.
Also how long has me smoked, and to what volume? After coming off pot I can tell a lot about it. Even though most effects are short term I think who you are as a person (character developement) suffers because of it.