How do you get a piplup in Pokemon Diamond?

ummmm im just gonna take it that you never played the game because you can pick piplup as your starter pokemon...you can chose piplup(my fave)(evolves into prinplup then empolean)or chose turtwig(then grotle then torterra)and finally chimchar(i hate the freakin thing!)umm he evolves into monferno then infernape*shudders*so hope i helped:D
You can either start off with it, breed, hack or trade.