Two people were punched at Shoreditch High Street station, leaving a woman with three broken teeth.
British Transport Police said a man was pushed by two people on the stairwell at the station at 7pm on April 22.
He reached the top of the stairs and then punched the two people - one in the face and one in the neck.
The woman suffered three broken teeth and a cut above her lip that required stitches. The second victim didn’t sustain any injuries.
The man is described as white, in his late twenties or early thirties with dirty blonde hair and a skinny build.
On the evening of the incident he was wearing a black hoodie and black jogging bottoms, both covered in white paint.
Police said they were keen to speak to anyone who was at the station that evening, or anyone with information, as they may be able to assist their investigation.
Witnesses, or anyone with information, can contact BTP by texting 61016 or calling 0800 40 50 40 quoting reference 890 of 22 April.
Alternatively, call Crimestoppers anonymously on 0800 555 111.