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.
'Look' how the Sheena Bora case has taken a toll on Indrani Mukerjea
Photos: Katrina Kaif, Parineeti Chopra, Shilpa Shetty's movie outing in Juhu
Birthday special: 14 Bollywood actors who made it big on TV
Photos: Vaani Kapoor, Poonam Pandey, Sana Khan at fashion event
Photos: Rishi Kapoor, wife Neetu, daughter Riddhima at book launch