just started playing pokemon red a week or two ago... i'm now up to the power plant bit but have flown back to the start to see if I can find the house/person that raises your Pokemon for you.

I left a Pikachu with him and want to get him back, but can't find this house.

Can anyone tell me where it is?

if i remember correctly, you can find him if you get to cerulean city and then start heading south, i might check the game later to give you more details.

Go South of Cerulean City. You should see some ledges which you can jump down but not climb back up. Jump down those ledges until you reach the house.

But be sure to have enough money, you'll have winded up quite a debt if you've left him for that long...