According to the police, the men first demanded Rs 5,100 and a mobile phone from her as a "penalty" because her friend was a "non-tribal" and then allegedly forced the girl and her boyfriend to strip and have sex in front of them, before taking turns to rape her.
Superintendent of Police Mayur Patel said 12 people have been arrested on the basis of inputs given by the girl and her friend.
The girl was taking a stroll with her boyfriend near the Sidhu Kanhu Murmu University campus at Dighi, 8 km from here, when at least six men intercepted them at the crossing of Ring Road and Dighi Road on Wednesday evening.
The men demanded Rs 5,100 and a mobile phone from her as a penalty for roaming with a non-tribal. Her boyfriend refused to hand over the mobile and assured them of giving them the money if he was permitted to call his friend.
But the culprits snatched her mobile phone and instead asked their friends to come to the spot, the police said.
The accused then allegedly forced the girl and her boyfriend to have sex in front of them at knifepoint by the side of the road. They then allegedly took turns to rape the girl, the police said.
The girl and her friend contacted their friends and relatives and reached Muffassil police station at around 11.30 pm that night and lodged a gangrape case, the police said.
The girl was sent to Sadar Hospital, where her condition was stated to be 'out of danger', police said.
While the girl is a native of Dumka, her friend is employed in Kolkata.
DIG Akhilesh Kumar Jha said, a case of gangrape has been registered against all the persons present in the scene of crime.