Pichu can be found in the First Forest . It is rare to spawn but keep a good eye out for it. Pichu is caught at Level 2. A simple Pokeball would be the easiest way to catch it. It only knows Scratch on capture. Pikachu will be very helpful on most of the gyms if you continue to train it.
Given: Scratch and Thundershock
Scratch: Starts off with it.
Thundershock: Learns it at level 7.
Evolves at level 15 into Pikachu.
Upon evolving, it changes Scratch into Tackle.