Austin Mahone, Astrid S, James Arthur, Old Dominion

Young Hollywood’s “Backstage Diaries” gives you an all-access pass to some of your favorite musical acts. This time around, we catch up with pop singer/songwriter Austin Mahone and his signature red microphone at the Fonda Theater along with a few of his devoted “Mahomies”; Norwegian singer Astrid S takes us through her soundcheck at the El Rey Theatre; at The Grammy Museum, British singer/songwriter James Arthur opens up about the meaning behind his smash-hit “Say You Won’t Let Go”; and country band Old Dominion show off their good-time vibes backstage at their album release party.