You have to move until the three Pokémon not reappear around you. This operation is repeated three times, the fourth time you do it, Pikachu also appear alongside the three Pokémon that can be caught as his starter Pokémon in Pokémon Go. Note that it may take a long time before it appears Pikachu, even 40 minutes sometimes.
Pikachu Super Star
Pokémon became world famous thanks to the TV series. In it, Pokémones communicated, saying the first syllables of his name, or the same full. But in the game Pokemon Go, the only creature that has this capability is Pikachu