Paul Pass, 49, was stabbed in his Gloucester flat in October by the pair, who used it as a drug-dealing base.
"Organised criminals" Abdulmalik Adua, 17, of Woolwich, and Rezwan Islam, 19, of Gloucester, "ruthlessly exploited and brutally killed" him, police said.
Bilal Ebrahim Moosajee, 19, of Gloucester, admitted manslaughter and kidnap, at an earlier hearing.
Adua and Islam were convicted of murder after a three-week trial at Bristol Crown Court. Islam was also found guilty of kidnap.
A 17-year-old boy from Gloucester was cleared of assisting an offender.
Det Ch Insp Mackay said Mr Pass was a "vulnerable drug user" who was killed by criminals who had "no hesitation in resorting to extreme violence".
He said: "Paul's friends wanted to reclaim his flat because they realised he was being taken advantage of.
"What they didn't realise was the lengths to which the people they stole from with were willing to go and the consequences it would bring."
The men were part of a drug-dealing gang from outside the county who were trying to establish themselves in the city, the trial heard.
They offered Mr Pass free drugs in exchange for using his flat as a base.
When Mr Pass's three friends broke in and stole the gang's drugs, the gang took revenge.
Islam and Moosajee arranged to meet Mr Pass and his friend Mark Andrews under the pretence of selling them more drugs, the jury heard.
Instead both men were frogmarched back to Mr Pass's flat where they were met by Adua.
Mr Andrews was stabbed in the hand and leg, while Mr Pass was hit over the head with a guitar and stabbed in the leg, which caused his death.
The three teenagers will be sentenced at a later date.
Two teenage drug dealers have been found guilty of the murder of a drug addict in a revenge attack.