San Joaquin County jurors convicted Anthony Waiters, 31, of all nine counts he faced, including aggravated mayhem, torture, kidnapping and false imprisonment of then-16-year-old Kyle Ramirez.
The teen was held captive in the Tracy home of Waiters' neighbors.
Ramirez, now 18, testified last month that Waiters, 31, cut him, lit his pants on fire and beat him unconscious between 2007 and 2008.
"They were all just laughing at me because I was trying to put the fire out," said Ramirez, then about 5 feet 8 inches tall and weighing 100 pounds.
The teen, now 6 feet 2 inches and 250 pounds, recounted other acts of cruelty, alleging Waiters once got a knife from the kitchen and cut his arm while others held him down.
"They cut my arm and poured bleach on it. It burned," he testified, showing jurors his scars.
The emaciated teen escaped by running to the backyard, jumping on a trampoline, hopping a retaining wall and running to a nearby health club in December 2008, wearing only boxer shorts and a shackle across his ankle.
Waiters' neighbors and the teen's then-legal guardian accepted pleas last month to more than a dozen felonies.
Michael Schumacher, his wife Kelly Layne Lau and Caren Ramirez pleaded guilty to charges that included use of a deadly weapon and causing great bodily injury to a child.
They could face at least 30 years in prison when sentenced Dec. 6.
Waiters is scheduled to be sentenced on Jan. 18.