A teenager suspected of knocking a Metro passenger out still hasn't been arrested.
Over a fortnight since the attack, British Transport Police confirmed it hadn't caught the suspected culprit.
A CCTV image was released last week of a man police believe can help with inquiries.
The assault happened at 8.08pm on Monday, April 1 at Brockley Whins station.
The teenager was reportedly smoking on the train when the victim asked him to stop.
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The boy departed at Brockley Whins, in South Tyneside, before allegedly striking the man following a row - before getting back on the train and heading to Monument.
Besides being left unconscious, the victim suffered cuts to his face and mouth and damage to his teeth.
Officers believe the person in the image may have information that could help their investigation.
Anyone who knows him, or who has more information about the incident, is asked to contact BTP by texting 61016 or by calling 0800 40 50 40 and quoting reference 564 of 01/04/19.
Alternatively call Crimestoppers, anonymously, on 0800 555 111.
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