Your question does not provide enough facts for a complete answer. If the dad simply fails to retrn the child, in violation of an existing court order, then you can petition the court for enforcement. If the "visitation" is simply an informal arrangement, with no court order in place, then you must file an action in court for custody, etc.
If the dad is able to either obtain a court order giving him custody, or is able to modify an existing order to give him same, then yes, you could be ordered to pay child support.
You should immediately consult with an experienced family law attorney in your area to determine your appropriate course of action.
If there is a Court order, then the court will help you get here back. If not, a court case needs to be started. Be aware that the longer you wait, the harder it will be to get her back. Call my office for a free consultation to discuss your options.