First you must enter the Burnt tower in Ecruteak City and they'll scatter off into random places, your job is to use your Poketch and see where they go.
You will have to either trade for Raikou or transfer from Diamond, Pearl, Platinum, HeartGold, or SoulSilver.
You cannot catch Raikou in Pokemon Black. You have to transfer it from Diamond, Pearl, Platinum, Heartgold, or Soulsilver.
he roams the map after you beat the game
Pokemon HeartGold and SoulSilver.
You cannot catch Raikou in Pokemon Diamond and Pearl. To get Raikou in Pokemon Diamond and Pearl, you must trade for one from Pokemon HeartGold and SoulSilver where it can be caught or transferring from Pokemon FireRed and LeafGreen.
Houndour, Houndoom, Lillipup, Herdier, Stoutland. Legends: Entei, Suicune, and Raikou. Find them in Pokemon Platinum, Black, Heartgold, and Silversoul.
Even if you leave Johto Entei and raikou will still be there.
You can't find raikou in ruby.
You can get it in Pokemon heartgold up the belltower ( but make sure you have a lv. 100 raikou
The best electric type Pokemon can be ether a Raikou or an Ampharos, I hope this helps.
You go to a mountain and catch raikou
Raikou is only found in firered and leafgreen if you chose squirtle as your starter Pokemon. Or you can get the purified raikou from Pokemon colosseum.