Harrison Ferguson was separated from his group after the performance at the Bowl on Saturday night, prompting the California Highway Patrol to activate a Silver Alert.
His family says he's 5 feet 10 inches tall and weighs about 165 pounds.
He was last seen wearing black and white Puma tennis shoes, light blue jeans, a white and burgundy striped shirt and a grayish blue leather jacket.
His family is offering a $1,000 reward in the case.
Anyone with information about his whereabouts is urged to call 911.