The 17-year-old was on the platform around 1:26 a.m. in the 200 block of South State Street when he got into an argument with a man and a woman, police said.
The man began chasing the teenager and hitting him with a broom while the woman stabbed him in the leg with scissors, police said.
The teen was taken to Northwestern Memorial Hospital where he was listed in serious condition, police said.
No one was in custody.
Area Three detectives are investigating.