Police sources say they are still looking for two others involved in the beating.
The assault happened on Oct. 18, just before 2 a.m. at the Elder Avenue subway station.
Police say the three assailants started an argument with a man and punched him in the face, causing him to fall into a moving train and then onto the tracks below.
The NYPD cannot confirm the 17-year-old boy's role in the attack.
The teen was taken into custody Wednesday and is charged with attempted murder and assault.