The accused, Rohit, used to work as system operator for a disc jockey. He is a native of Palwal in Haryana, but stayed at Patel Nagar in Delhi, they said.
The incident occurred last night when the girl's family went to the hotel in sector-15 of Gurgaon to attend the wedding ceremony of a relative there, a police official said.
"The girl, who playing during the party, accidentally entered men's toilet, where the accused gagged the minor and sexually assaulted her," he said, adding, "She somehow managed to escape and told her father about the incident."
An FIR has been lodged against the accused under Protection of Children from Sexual Offences (POCSO) Act, the police said, adding investigation into the incident is underway.