Oh magneto,

I must admit that I haven't read the comics, but from what I've heard, isn't magneto's "magnetism" more of a manipulation of molecular electromagnetic forces? In which case it doesn't matter if it's nonmetal, as long as it's matter he can manipulate it.

There was one comic where Iron Man made a metal-free suit just to fight Magneto, it was made of carbon-fiber composites and ceramics. Magneto picked up every car within a mile and slammed them into him all at once.

Also in the Avengers vs X-men storyline, Magneto channelled the magnetic fields of other planets and hit Stark.