Police have constituted a special team to investigate. The woman reached Manali, some 250 km from the state capital Shimla, Monday.
The victim lodged a complaint with police that she was picked up by the men, aged between 18 and 25 years, in a commercial vehicle when she was going back to her guest house after visiting a friend early Tuesday, Superintendent of Police Vinod Dhawan told IANS.
He said the accused took the victim, who was on her maiden visit, to a secluded spot and gang-raped her.
Later, the victim was dropped on the outskirts of the town.
"She was medically examined and the report confirmed sexual assault. We have zeroed in on the suspects as per the information provided by the victim," Dhawan said.
No arrest had been made so far.
In the complaint, the woman reported theft of cash and valuables.
Meanwhile, police chief B. Kamal Kumar told reporters in Shimla that a special investigative team was constituted to speed up the probe.
Earlier, an 18-year-old British volunteer teacher was raped by two cab drivers in Palampur town in Kangra district in 2009.