What does mi tampoco mean in English?

Answer 1

"mí tampoco" is incomplete and would need a preposition such as "a mí tampoco" or "para mí tampoco". However, the "mí tampoco" part of those larger expression is "me neither" or "also not me".

Answer 2

"Mí tampoco" doesn't make much sense by itself. It can, however, be part of a longer expression; for example, "A mí tampoco" would mean "Neither to me".