Find a therapist now. But the situation is what it is, so let's start from there. Work out the visitation arrangement and try to stick to it with reliability and consistency and look to other family members, teachers, or coaches who can provide some role modeling. Work on communication and consistency in your relationship with your child. There are many interesting articles on adolescence and child development.
Identity formation is the major challenge of adolescence.
You can help by providing constructive and wholesome opportunities where your child can be successful. This might be sports, youth groups, music, dance, or art. Try to help your child get into situations that they are interested in that are the right level to insure success and allow them to function independent of you and their immediate family. Be encouraging and forthcoming in your praise and reinforcement. Allow them increasing levels of freedom and responsibility as long as you have a good chance of success.