Peter Pan is somewhat more random when it comes to appearances than other characters.
In WDW you can often find him near the bridge to Adventureland.
In Disneyland Peter does often come out to play, but it is never guaranteed you will find him. The best place to look for him is at Refreshment Corner on Main Street, or wandering around Fantasyland.
At Disneyland Paris Peter appears in a multitude of places, including Adventureland by Colonel Haithi's, by "it's a small world" and his attraction in Fantasyland.
In Tokyo, Peter is often out in Fantasyland.
Peter does not meet in HKDL.
Peter does appear on select Disney Cruise Line sailings. Check your Personal Navigator for details.