Jody,
When my difficult child was just turning 16, he freaked us out by doing the exact same thing. He stopped paying any mind to school, wanted no part of us or our home, and he left the house constantly to hang out with friends and to smoke pot and drink. It was as though he was possessed. We literally lost control of him and could not reach him at that age. CPS actually said he was "unparentable" at that time.
It got much worse before it got better, but watch out for the pot smoking, because where there's smoke, there's fire (no pun intended).