The live stream – originally posted by Brittany Herring but since deleted – shows the victim, who officers say has special needs, cowering in a corner with his arms tied and his mouth gagged.
He was filmed as he is kicked and punched by the gang, who can be heard shouting “f*** Donald Trump. F*** white people”.
At one point they cut the man’s hair until his scalp bled before flicking cigarette ash into the wound.
Police Superintendent Eddie Johnson said at a news conference that four suspects, two males and two females, are in custody. Formal charges have not been filed.