Police were seeking the public's help in identifying juveniles seen in a viral video posted on social media sucker-punching a mentally challenged man in the city's Germantown section.

The 30-second video, recorded in slow-motion, shows the man smiling and apparently distracted as a young teen boy moves in from behind and punches him hard on the left side of his face.

The victim appears shocked by the attack, which happened at Chelten Avenue and Knox Street, when  a second older male pursues him and punches him around the his right ear. There are five males visible in the video. The youngest is seen laughing hysterically.

Gerald Andrews Sr., 48, said the victim was a co-worker at a ShopRite in Cheltenham and identified him by his first name, Mark.

"He keeps that smile on his face. He wants to talk sports. He's a good guy," Andrews said Monday night about Mark.

Andrews said he learned about the video from another co-worker and posted a copy Monday afternoon on Facebook.

"It's heartbreaking," he said of the attack.

As of 9 p.m. the video had been viewed more than 100,000 times and had been shared nearly 3,900 times.

Andrews said he did not know where the video was originally posted.

Northwest Detectives Division is investigating the assault, said police spokesman Sgt. Eric Gripp.

"Obviously, what is depicted in the video is very disturbing," Gripp said. "We would implore anyone who has info on the video, or who knows the identity of the victim to reach out to police."