You can get it in GTS or trade it from Silver or Gold
You can't catch a Lugia in pokémon platinum. If you would get a Lugia on platinum you should link it.
You cannot find Lugia in Pokémon Platinum.
Shadow Lugia does not exist in platinum.
Sorry. You cannot obtain Lugia in Platinum. You have to trade it from HGSS.
You cannot find Lugia in Pokémon Platinum.
You don't. Shadow Lugia is not available in Pokemon Platinum.
You don't. Shadow Lugia is not available on Pokemon Platinum.
Lugia is not available at all in Platinum, so hacking is the only way.
No
MAYBE
The only way to get Lugia in Pokemon Platinum, is to use Action Replay, or to trade from other games.
shadow lugia is not in Pokemon platinum