Sgt. Randy Fincham said the woman was walking near Granville Street and Broadway around 4 a.m. PT on Jan. 1 when a man grabbed her.
Two men at a nearby bus stop ran to help her as the suspect fled, but the 38-year-old victim didn't get their names.
"These two men should be commended for their actions. These men are great citizens," Fincham said. "They came forward and scared this suspect away before he could do more harm than he did."
The suspect is described by police to be a white man in his forties, about six feet four inches with a slender build. He was wearing a black hoodie.