Did Megan follows play in I am number four?

The movie "I Am Number Four" is based on the book series of the same name by Pittacus Lore (a pen name for James Frey and Jobie Hughes).

In the movie, the character of "Number Four" is played by Alex Pettyfer. Megan Fox is not in the film.

It's possible you're thinking of a different movie or perhaps you're mixing up the actors or the title.