The incident came to light yesterday when the girl, a class 12th student, narrated her ordeal to her mother who filed a complaint with the police.
According to the complaint, the victim was first gangraped on December 12 last year when she was returning from school, Additional Superintendent of Police Ramji Singh Yadav said.
The three accused abducted her and gangraped her one by one, Yadav said, adding, they also made a video clipping of the crime.
The accused had raped the girl several times since then on the pretext of uploading the clipping on internet, the ASP said.
The girl eventually reported the incident to her mother yesterday when she started getting renewed threats and when some more youths joined the trio, he said.
One of the youths has been arrested for raping and blackmailing the girl, Yadav said, adding, search is on to nab the other accused and to recover the mobile phone carrying the clipping.
The girl has been sent for medical examination, the ASP said.