Sixty-nine-year-old Paolo Meraglia, who claimed to be a sorcerer, abused the girl for months.
The victim's boyfriend at the time, a 19-year-old; his mother; and a 73-year-old friend of Meraglia also took part in the abuse, police said in a statement.
Officers on Monday arrested the three men for gang rape, aggravated by the use of sedatives and the fact their victim was a minor. Police did not say whether the mother of the girl's ex-boyfriend would face charges.
The girl began visiting the 'wizard' in September 2015 along with her ex-boyfriend and his mother, police said.
"He convinced the girl she was the victim of strong 'negative forces' and consequently convinced her to undergo 'purification rites' consisting of sexual intercourse, sometimes in a group," they said, adding that the victim was "semi-sedated" when the abuse took place.
The abuse took place in an attic in Turin and lasted for several months before the girl contacted police last September, after the men had reportedly threatened to distribute videos of the rapes.
"In the course of the investigations, the existence of a sort of hierarchy emerged," police said. Meraglia was known as the 'Master' and appeared to be in charge of the group, with the others known as the 'Apostle', the 'Vestal Virgin' (the victim), the 'Catalyst' and the 'Maid'.
A search of Meraglia's home also revealed several items thought to have been used during the 'rites', including hand-written incantations and tarot cards.
Police are now working to establish if there were any further victims.
A similar case in Palermo last year saw a priest and soldier arrested for sexual abuse after they had touched the genitals of women and children under the pretext of liberating their victims from demonic possession.
Although priests are permitted by the Catholic church to carry out exorcisms, the rite should only occur with authorization from the diocesis, and the Palermo priest was not recognized as an exorcist.