I had a situation sort of like that with a bunch of college kids on spring break.
We were a last minute equipment change (JFK/CUN) and therefore had to make a fuel stop in Sanford, Fla.
As the refuelling was going on, the F/E and myself smelled cigarette smoke coming into the cockpit from the cabin. (The pax were remaing on board.
My initial plan was to go back and cleverly ask them to stop smoking, as we were almost ready to go, and Cancun was only another 50 minutes away.
But when I got back to where the smoke was, I noticed several cigarettes ground out on the carpet. (they didn't even use the ashtrays) Since no one would 'fess up, I decided to put everyone off. They wouldn't go, so I had to call for police intervention.
I explained to the tour leader that when whoever was smoking fessed up, they would stay behind and everyone else could go on with us, but they had to find the persons within 15 minutes or we would be out of duty time and then no one would go.
No one owned up to smoking, but one poor girl pointed one of the guys out to a cop, who told me, so I left him and took everyone else. This guy then had the ba!!s to say he wasn't the only one and it wasn't fair. I told him to tell me who the others were so then he could have some company.
The tour director wanted to know what to do and I told him to tell the other offenders who weren't caught to hand over $100 each to his buddy who was caught so he could buy a ticket to join the group the next day.
In the USA smoking on the a/c is a federal offense, so there's a little more leverage than other places where it may only be a company policy.