Where do I find Pikachu? I want a hat!

Meet up with a few friends, go to a dual/triple PokéStop spot where it's comfortable and lure the PokéStops (each one of you should lure a Stop).
I did this and observed an increased Pikachu spawn rate out of lured Stops. Give it a try!

I opted to walk a half-hour to work today rather than drive (and there are very few pokestops on the way). I found two Pikachu on the way, neither anywhere near a pokestop.

It seems like it may work to go to less popular areas. Just a thought if other stuff doesn't seem to work for you.

I hadn't seen any until this morning, when I ran into two in less than an hour. One at a pokestop and one at a random corner. Makes me wonder if they bumped up the spawn rate...