The jury in Akron deliberated 20 hours over four days before finding Brogan Rafferty, 17, of Stow guilty of multiple counts of aggravated murder, attempted murder, robbery and kidnapping, the Akron Beacon Journal reported.
He faces the possibility of life in prison when he is sentenced Monday by Summit County Common Pleas Judge Lynne Callahan.
Co-defendant Richard Beasley, 53, who authorities say was Rafferty's mentor, is to stand trial in January.
Jurors Dana Nash and Michele Lewis, both of Akron, told the newspaper they were led to find Rafferty guilty because they found his testimony contradictory.
"We was kind of skeptical," Nash said. "Because he was kind of contradicting his self during his testimony and some of his interviews. Luckily, we took good notes and the evidence was there.
"We were trying to be fair and we were fair. We came up with the right decision. It was very difficult for us because, like I said, he's a child and it was very hurtful."
The victims responded to a 2011 help-wanted ad that promised $300 a week and a trailer to live in to oversee the use of an expansive property in Noble County.