Drones represent an immediate danger to the participants and spectators of a soccer match. Drones are prohibited at all USSF youth soccer matches by US Youth Soccer Policy.
When a referee sees a drone flying in the vicinity of the field, the referee needs to treat the drone just as a referee would if they saw lightning. Stop the match immediately. Notify the coaches why you are stopping the match and tell them the match will not continue until the drone is no longer flying in the vicinity of the field.
It is not up to the referee to identify who is flying the drone or ask them to stop. That responsibility is on the coaches, field marshals or complex staff.
The USSF policy can be found here: USSF Policy on Drones