Eimer, who hails from Virginia, had been asking the singer to be her date for the high school event for several years through her website but Bieber had to decline the invite because of other commitments.
"I couldn't make it to prom so I said I need you to fly to the Billboard Awards and you can be my date. She is a big fan and I thought it would be fun," Bieber said.
Eimer thanked the singer on Twitter saying, "Thank you so much for an amazing night! I had the time of my life. Not gonna lie, I am sad today is over. It was so much fun," she said.
Photos: Deepika Padukone, Neha Dhupia and Soha Ali Khan at event
In pictures: 15 facts about kissing that will surprise you
Birthday special: Shahid Kapoor's best performances in Bollywood
Photos: Kim Sharma, Sagarika Ghatge, Zaheer Khan at launch in Mumbai
Photos: Kangana Ranaut looks pretty in pink