私も.

I agree Ryoko. 私もです is more useful than 私もそうです. Like Ryoko said, it really depends on the context.

It depends on the context. In the casual conversation, we say 私も but in the formal conversation, it depends on the context. Generally, we say 私もです/ 私もそうです etc. *私はも doesn't exist. Espero que te ayude.

あたしも = girls only （sounds可愛い） わたしも =boys and girls