Just before 6.15pm on Monday British Transport Police were called to the line close to South Elmsall following reports of a person on the tracks.
The boy was treated by paramedics for serious electrical burns.
He was taken to hospital where he remains in a critical condition.
Anyone with any information on this incident is asked to contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting 412 of 03/10/2016.