The Pikachu family- Pichu, Pikachu, and Raichu- are not legendaries. Pikachu is really just the Pokemon Franchise's mascot.
Pichu evolve only when they really love their trainer. To make it love you, you should keep it in your party, have it battle, do NOT let it faint, and give it the item Soothe Bell if you have it. When it loves you enough, it will evolve at its next level up UNLESS it is holding the item Everstone.
Hope I helped. :)