It is possible to do a 50/50 custody regardless of living in different states if: (1) you are on a border or (2) your child is not yet of school age. In Northern Kentucky there are times when parties equally share custody with one living in Northern Kentucky and the other living in Cincinnati. If the child is not of school age, you can have week on/off or month on/off and living apart. Once the child starts school, this becomes a significant problem.
The best bet of the father is to file a Motion for Contempt to begin. This would likely be filed with a Motion to Modify the Parenting. Since the mother moved away, it is possible that the father may be granted primary custody. Typically when one party relocates, the court must then amend the parenting schedule to accommodate the child. The primary residence, as well as the modified parenting schedule, is determined by the standard of "best interest of the child."
Often it is best that the child remain in the current school system, around family and friends and doing the same activities that he was doing prior to the move. Obviously the age of the child, the time with each parent, the activities and school all play a factor into a Judge's decision.
You/your friend should hire an experienced family/domestic law attorney as soon as possible. Sitting on your hands while not seeing the child or while the child gets adjusted to the new locale is disfavored by the courts. The sooner something is filed the better the chances of the father getting favorable results.