The singer, who wore a black bra and leather pants for her party on Saturday, was photographed smooching with the 18-year-old Victorious actor against a banquette at Trousdale nightclub.
And in between the kissing, the birthday girl even found time to have a dance-off with Ke$ha.
An eyewitness told Us Magazine the pair flexed their moves to Pink's Raise Your Glass, and were quickly joined by everyone else on the dance floor. 'She was so busy dancing and hanging with her friends,' the source said.