It was originally posted on Facebook Live by Brittany Herring but has since been deleted from her social media page.
The victim, who police say has special needs, was seen cowering in a corner with his arms tied and mouth taped shut.
He was filmed being kicked and punched before he had his hair cut until his scalp bled.
The victim also had his clothes cut and had cigarette ash flicked over the wound on his head.
Someone can be heard in the footage yelling "f*** Donald Trump. F*** white people".
"It's sickening,' Chicago Police Supt. Eddie Johnson said on Wednesday night.
"It's makes you wonder what would make individuals treat somebody like that. I've been a cop for 28 years, and I've seen things that you shouldn't see in a lifetime, but it still amazes me how you still see things that you just shouldn't.
"I'm not going to say it shocked me, but it was sickening."
Police said the victim was treated and released from hospital into the care of his parents.
Chicago Police Cmdr. Kevin Duffin said the victim was an acquaintance of one of the offenders and they had attended school together.
"Apparently, they met out in the suburbs. These subjects then stole a van out in the suburbs and then brought him into Chicago," he said.
"It is quite possible it is a kidnapping. (The victim) is traumatized by the incident and it is a little tough to communicate with him."
The victim was found walking distressed and disoriented on the street by police on Tuesday night.
Police said they were later called to a battery at a nearby residence and discovered signs of a struggle and damage to the property.
Authorities linked the struggle to the disorientated man and later became aware of the social media video showing the violence.
Police arrested all four people shown in the footage and they remain in custody.
Authorities expect to lay formal charges within the next 24 hours.
Police said it was too soon to make a determination if the attack was racially motivated.
They added that the four offenders had not said anything that led them to believe the attack was politically motivated.
The investigation is ongoing.