Police are searching for a woman who recorded a serious assault in downtown Toronto on her cellphone in hopes it will help locate a suspect.

Investigators have released a surveillance video that shows 28-year-old Brendan Byrnes fighting with a man at the southern corner of Yonge and Edward streets around 7:30 p.m. on June 20. Byrnes, the father of a six-year-old boy, had just attended a free concert at Dundas Square.

The man police want to speak with appears to punch Byrnes at least twice, knocking him unconscious to the ground.

Byrnes was taken to hospital with life-threatening injuries, which have since stabilized. He emerged from a coma on Wednesday.

Police believe dozens of people witnessed the assault and some even stopped to videotape Byrnes as he lay on the sidewalk. But no one stuck around to help investigators.

The surveillance video also shows a young woman using a cellphone or BlackBerry to record the incident.

"We'd like that person to revisit their actions that day and come forward," Det. Sgt. Deborah Abbott told reporters on Thursday. "Whether they've lost the video or not, that person is still a witness."

Byrnes' father Jim has been at his son's bedside for 11 days. He said his son still doesn’t know what happened to him.

"He doesn't know who he is. Sometimes he knows who we are. Sometimes he doesn't," he said.

"It feels like it's becoming very much a YouTube world that we want to be witnesses to society rather than members of it and we're all in this together," Byrnes said. "And I think people forget that sometimes."

He said a stranger dressed in hospital scrubs did stop and aid his son until an ambulance arrived. But the stranger also vanished soon afterward.

The suspect is described as white, mid−20s, five-foot-nine, 150 to160 pounds, with long brown hair in a ponytail and facial hair. He was last seen wearing a black T-shirt with a large circular white design on the back and black pants.