Two Britons, both 18, were allegedly attacked by six men of “Arab appearance”, and were left needing hospital treatment.
The gang allegedly set their sights on the two British men the minute they boarded a tram that was going from the city’s Cathedral Square towards the neighbourhood of Riehl in the north.
The two Brits got off at Slabystrasse and walked towards the Muelheim Bridge over the Rhine, when the gang attacked in August last year.
Cologne police have released images of men they want to question
Cologne police have released CCTV images of the men
The gang reportedly punched and kicked both men multiple times, stealing a mobile phone and a wallet.
The migrant mob were said to be between 18 and 20 years old, with one of them described as being "particularly large", while the others were said to be of normal build and "Arab-looking".
Cologne police released the footage of the suspects in the hope that witnesses might recognise the people on public transport.
CCTV footage of the men Cologne police want to question
Germany has a very strict privacy laws which often forces police to pixelate suspects' faces.
Authorities sometimes censor such footage out of fear it will incite racial hatred, as happened when a politician prevented the police from posting an appeal for help in the search for the suspect in the Berlin Christmas attack.
Cologne: Sex Attacks and Robberies
Tue, January 12, 2016
Thirty-one suspects, including 18 asylum seekers, are under investigation over offences including sexual assault and theft in Cologne on New Year's Eve. Far right protestors in Lepzig have rallied against refugees and German chancellor Angela Merkel.
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Protestors in Lepzig rally after over 100 women were sexually assualted on New Year's Eve
However, in this high-profile instance the images were released unpixelated.
The assault comes after more than 1,000 women were sexually assaulted during the Cologne migrant sex attacks.
Reports compiled by detectives lay bare the true scale of the horrific assaults, when a crowd of 1,000 migrants groped and raped women out celebrating New Year’s Eve.
One of men wanted by Cologne police
One of the men wanted by Cologne police
The gang attacked two British teenagers who were on holiday in Cologne
The attacks sparked anger in Germany just months after Angela Merkel controversially decided to welcome more than a million migrants and refugees from the Middle East and North Africa.
It led to a backlash among the German public and in the aftermath the German Chancellor made a series of U-turns on her open attitude towards migrants.