The 20-year-old former Disney star also took the unidentified man back to her hotel after the party, reported New York Post online.
Gomez stayed at the event's after party until 2:30 am and was seen entering her car with a "scruffy young guy", according to an eyewitness.
The mystery man was reportedly wearing a white flower from the singer's headband in his hair.
Gomez used her performance at a Unicef benefit to take digs at her ex-boyfriend, Bieber by singing the notorious break-up songs, 'Cry Me A River' and 'I Knew You Were Trouble'.
"I have been through a lot the last couple of months. It is been sad and cool, but interesting. This song definitely speaks to me," Gomez told the audience.
At the end of the song, she let out a laugh and said, "Well, enough of that."
