Three girls and a male are being sought over two separate bottle attacks in train carriages which left three passengers hospitalised.
A group of six suspects travelled on the Dartford to Charing Cross service, between Kent and London, in both directions early on Saturday evening.
One woman who boarded the London-bound service at Slade Green station at the same as the group was threatened and shoved by one member of the group after asking them to quieten down at around 5.45pm.
She retreated to another carriage but was followed by the group who allegedly started hitting her with glass bottles and kicking her in the head.
The victim was given first aid and rushed to hospital after getting off the train at Erith station while the group stayed onboard.
Shortly before 7pm on the Dartford-bound service, the group began verbally abusing a couple, who were not known to them.
A girl from the group started hitting one of them, a female, with a wine bottle, before the rest of the group began attacking both of them.
Other passengers managed to pull the couple to safety, and were also assaulted in the process.
The victims alighted at Belvedere and taken to hospital while the group remained onboard.
Four CCTV images showing three young females in dark clothing and a male in a hat and dark hooded garments have been released.
Anyone who recognises those pictured or has any information has been urged to contact British Transport Police by texting 61016 or calling 0800 40 50 40 quoting reference 492 of 11/09/21.