Seven persons, aged between 19 and 32 years, have been arrested in this connection and a search is on for the main accused and some others, who are absconding, they said.
Police said despite the torture she underwent, the 15-year-old girl had appeared for the just concluded Class X examinations this year as she was keen to write it.
The girl, who stays with her mentally challenged mother and a cousin brother, works as a cinematic dancer for a living.
While the latter is among those who have been arrested, the former is at large, police said.
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The accused also recorded the heinous act on their mobile phone cameras and began threatening the girl that they would release it if she did not give in to their demands for sexual favours.
Police said the girl had on several occasions been tortured when she tried to resist her tormentors. There were several injury marks of cigarette butts on her body. She was also forced to consume liquor and smoke ganja, they said.
The plight of the victim came to light on March 30, when she was physically attacked by the gang at Paripally on the outskirts after she refused to heed to the demands of her tormentors.
When local people gathered and questioned the men, they fled from the spot. Police took the girl to the police station where she narrated her torture.