Justin Bieber
The clothes start to come off...
Nick Jonas
The "Jealous" singer packs a mean onstage presence.
Taylor Swift & Alana Haim
The besties cheer on Calvin Harris while he performs on stage. Swift and Harris have sparked romance rumors but have not confirmed a relationship.
Kanye West
The hip-hop star performs on stage.
Adam Lambert
The American Idol alum gets a personalized BigTruck Brand hat before introducing a band onstage.
Meghan Trainor
The singer sports a golden look on stage.
Taylor Swift
The singer cheers on Calvin Harris.
Fifth Harmony
Before performing their hits including "Sledgehammer" and "Miss Movin' On," the girl group snacks on Sabra backstage.
Jonathan Scott
The Property Brothers star gets super fierce at KIISFM's gifting suite.
Kris Jenner & Big Sean
The Keeping Up With the Kardashians momager is spotted in the audience watching Kanye West .
Sophia Grace
Before enjoying her favorite acts, the YouTube star does some serious shopping at KIISFM's gifting suite.
Calvin Harris
The singer and DJ performs on stage.
Adam Lambert
The glam rocker takes the stage.
Fifth Harmony
Singers Lauren Jauregui, Ally Brooke, Dinah-Jane Hansen, Camila Cabello and Normani Kordei perform onstage.
Ellen K & Ryan Seacrest
The stars of KIIS-FM's On Air With Ryan Seacrest pose for pictures before introducing Nick Jonas and Justin Bieber.
Tori Kelly
The "Nobody Love" singer gets beautified with the help of Priv backstage.
Meghan Trainor
The "All About That Bass" singer walks the red carpet.
NEXT GALLERY: More Singers Performing Live