If the computer she used is not owned by her then any information or subsequent accounts created on or used on that computer are not exclusive to her only. If it is a family access computer then they can do what they can to get on without worry of legal action from a 16 year old.
Even so, if the computer was purchased by her there would still be very little chance that a judge would rule in the case of the daughter given that she is a minor and the parents have the best interest of the child in mind.
Ok, on topic. It would be helpful if you could find the town or the county where the parents live. Just calling State and telling them your problem won’t do much unless you have a location to give them. Do you have his last name? Cell number? Names of friends/acquaintances? Have you looked up her calls on her cell phone through the phone company?
Maybe you should have a friend try and contact her for you. See if the friend can feel out where she is and what she intends to do. Just make sure the friend is one that realizes she’s doing something dumb and wants to help you out instead or tip her off your trying to find her/ cme and get her.