Durham Regional Police said officers responded to a bar near Park Road South and Malaga Road at around 2:30 a.m. on Sunday.
Police said a 19-year-old woman was located with life-threatening injuries and was taken to a Toronto-area trauma centre.
In an update Monday morning, police said she remains in critical condition.
Suspects fled in a black pickup truck before officers arrived, police said.
Any witnesses or anyone with video footage is being asked to contact police at 1-888-579-1520 ext. 2765 or Crime Stoppers anonymously at 1-800-222-8477.