Club Penguin Island is different than the Classic version, where on Club Penguin Island, you can always find the Characters in their spots at all times, unlike at special times on Classic. Finding and Interacting with Characters, now is how you can began their Adventures, if you have a Membership.
Now Rockhopper is one of the first Characters that you see in the Welcoming Adventure, but after you have finished the Starting, you can find him on The Migrator (his ship), on the left side of Beacon Boardwalk. Just use the Interaction button to speak with him.
Until next time,