Where Do I Find Pikachu In Soul Silver?

You can find it easily in viridian forest, but only if you take a other electric pokemon to walk with you. I did that and I caught 3 in a row and they said that there were only 2
! Ampharos walked with me. So maybe this is usefull I bet it is :)

First you must beat the elite 4. Than you go to viridian forest in kanto

...viridian forest/pokewalker route yellow forest/resort pokewalker route(80,000 watts+national dex)

I've been wondering around that place for like 4 hours and not 1 pokemon related to pikachu or even a pikachu

You get picachu in yellow forest on the poke walker   I have yellow forest on my hg but  on my ss I did not find picachu in viridan forest

You take your partner pokemon and you walk through grass and hope you get lucky

Viridian forest its so obvious thats what everyone else is saying and its true to heck with the pokewalker