Where to find Empoleon in Pokemon Platinum?

Their is only two Empoleon's in the whole game. One is if you chose Piplup as your starter Pokemon and leveled it up to level 36, then it will evolve to Empoleon.

If you didn't chose Piplup as your starter Pokemon then a trainer on Victory Road has it in their party.

if you chose chimcar your rival will have it too