Disney Channel has announced kick-off for a nationwide casting search for High School Musical 4, a follow-up to the wildly popular High School Musical franchise (which just celebrated its 10 year anniversary with a cast reunion). The Disney Channel Original Movie franchise concluded in 2008 with the theatrical release of High School Musical 3: Senior Year, which bid farewell to stars Zac Efron, Vanessa Hudgens, Ashley Tisdale, and more.