Each book adding a new POV is exactly what Patrick Ness did in the Chaos Walking Trilogy, and I really liked it. His main character stayed the focus of the story, but the other POVs added depth and complexity.

I think multiple third is more what we are used to, at least in adult novels. I don't know about YA, though. It seems that they stay more focused on one character. But Chaos Walking is YA, too, so it can be done successfully. :-)