Pikachu is one of several Pokemon that uses an Evolution Stone to evolve. In this case you need a Thunder Stone. If you are playing a Gen 1 game, you can buy one for 2500 at the Dept. Store in Celadon. If you are playing a Gen 2 game, you can get one from Bill's grandfather or buy one with points at the Pokemon-a-thlon (HG,SS only). Gen 3, I think you can find one in the Underground of Mauville. Gen 4 and 5, I'm not sure :P
Pikachu evolves when you give it a thunderstone.
LEVEL 26
Level 32.
Finneon evolves at level 31.
lvl 20
Evolves via trade, not by level!
Trapinch evolves into Vibrava at level 35.
Yes you just have to raise its level
Pikachu learns Thunderbolt at level 29.Pikachu learns Thunderbolt at Level 29.
Pikachu learns slam at level 21.
Pikachu learns thunderbolt at level 26.
Pikachu doesn't evolve by level, you have to evolve him with a thunderstone.