What is the first step to take if the father stops paying child support because his 16 year old daughter doesn't want to see him.

The first step would be to make a written request to the father for the payment.  If father does not pay, then you may file a Petition for Contempt.  The court has several remedies available, such as garnishing father's wages, intercepting his federal income tax refund and awarding you attorney fees and costs for his violation.  Many thanks.