The teenage couple reunited at New York nightspot the Glass House after each had performed live on TV shows - 17-year-old Justin on Dick Clark's 'New Year's Rockin' Eve' and his 19-year-old girlfriend on MTV's NYE in NYC broadcast - and wasted no time in getting on to the dance floor.
A source told E! Online: "Justin danced with Selena, showing off, picking her up and swinging her around like it was 'Dancing With The Stars'."
Following his dancefloor exploits, the 'Never Say Never' hitmaker later took over the DJ both, where he played 'Happy New Year', his new song with friend Jaden Smith.
Meanwhile, Justin has now amassed 16 million followers on twitter, making him the second most followed person on the social networking website behind Lady GaGa, who has 17.5 million followers.
He tweeted about reaching the milestone: "2012 is going to be so good. #16millionbeliebers, and I can already tell this year will be as good if not better than 2011."