The video, obtained and published by the New Zealand Herald, shows the man being attacked by the vigilante group who believed he "was trying to meet a 14-year-old girl for sex”.
The schoolboys told the man they would not report him to the police if he ate some cat food.
The video also showed the man on the ground before he was dragged out onto the street, the Herald reported.
At least one of the boys from the group appears to be wearing a Christchurch Boys’ High School uniform.
The group continued to kick him for some time, before forcing him to eat pet food.
CBHS headmaster Nic Hill said he was made aware of the video by the Herald last Tuesday.
Hill told the Herald the school was working with McDonald’s Riccarton and the police.
He said last week the school had been in contact with the police and meetings were under way with students who may have been involved.
"This behaviour is not on,” Hill told the Herald.
"I’m incredibly disappointed to see it, there’s no excuse for any of this.”
Detective Senior Sergeant Karen Simmons said police “have received a report of a video depicting an assault and are making inquiries to determine when it occurred and who was involved”.
“A local high school is assisting with our inquiries,” she said.
