Hi Butterfly,
I'm in a similar situation to you in that I'm trying to help find loved one a place to go after rehab. Your grandson really belongs in a rehab facility. Does he have insurance?
From what I understand the state of GA does not have programs for inpatient care, but he might be eligible for outpatient services. This state is severely lacking in it's resources for people without insurance or rich family members.
I strongly suggest looking into the Salvation Army's rehab program. It's free and it has a very good success rate. That said, they are selective about who they take in. If your grandson isn't serious he'll get nothing out of any program.
Another resources is the United Way. Dial 211 and explain the situation, they may have some helpful suggestions for you.
Best of luck to you.