Abandonment

[JLang1987]

My ex girlfriend has custody of my 2 year old son. She recently decided to move out of Iowa to Illinois and leave my son in the custody of her grandmother. She has been gone for over six months but i cannot prove without a dout that she hasnt had any contact. Is this considered abandonment? I dont wish to pursue custody. She is still recieving my child support and hasnt shown any intentions of coming back or using it to provide for our child. What can i do from a legal standpoint?