Find the Missing Pirate is a quest given by Horace Horsecollar in his Detective Agency on Mean Street, after returning from Tomorrow City. This quest is given alongside the Detective Mickey II quest.
When Mickey talks to Horace, he will inform Mickey that one of his clients, Pirate Moody is wondering where his cousin, Rigger Greene has gone. He states that Rigger Greene was supposed to return to Ventureland with the other pirates, but never made it. He asks Mickey if he is heading to Ventureland, could he try to find out what happened to Moody's cousin.
Rigger Greene is located in the Pirate Voyage, locked behind a gate which was meant to be a trap for Bashers made by Gremlin Erik. Mickey needs to free Erik, who will explain that Greene stumbled into the trap and locked himself inside with treasure, while Erik was stuffed in a cage by Bashers. Erik will unlock the gate, setting Greene free. Mickey can go inside to have some of the treasure, which will include a Silver Pin. Rigger Greene will then return home to OsTown to be with his cousin Moody.