Officers investigating "Muslim vigilante" attacks are appealing for a victim who was abused by the gang for being "gay" to come forward.
Scotland Yard says the man is crucial to their investigation into a number of incidents where a gang calling itself Muslim Patrol has harassed members of the public.
Videos of the attacks in east London where the self-styled gang appear to have started to operate have been posted on YouTube.
The police are appealing for the man in the footage, titled Muslim vigilantes in London harass and taunt gay male, to contact them.
In the film, the gang can been seen to abuse and intimidate the man using homophobic language, shouting: "Get out of here you f** ... don't stay around here any more."
Investigating officers from the Community Safety Unit on Tower Hamlets borough said they are unsure where and when the video took place.
In a second video, posted online, men from the gang in Whitechapel, east London, tell another man "no drink in this area, it's a Muslim area" before ordering him to pour away his alcohol.
Another video posted on YouTube featured a woman wearing a miniskirt being told not to "expose" herself near a mosque.
Detective Chief Inspector Wendy Morgan from Tower Hamlets borough said: "The Met takes such homophobic behaviour very seriously.
"This man is a crucial witness in the investigation and would encourage him and anyone else with information relating to this incident to make contact in confidence as soon as possible."
Additional police patrols are being mounted across east London to reassure the public.
Four men have been arrested in connection with the investigation.
A 22-year-old man was arrested in Acton, west London on Sunday, and a 19-year-old man was arrested on Wednesday after going to an east London police station.
The pair were arrested on suspicion of causing grievous bodily harm and public order offences and were bailed to return to an east London police station in February and March pending further inquiries.
Two other men, aged 25 and 29, were arrested earlier today and remain in custody.
A police spokesman said: "The Metropolitan Police Service takes these incidents very seriously and is pursuing various lines of inquiry with a view to identifying and prosecuting the individuals concerned."
Islamic leaders in east London condemned the vigilantes.
A spokesman for the East London Mosque said: "These actions are utterly unacceptable and clearly designed to stoke tensions and sow discord. We wholly condemn them.
"The East London Mosque is committed to building co-operation and harmony between all communities in this borough. The actions of this tiny minority have no place in our faith nor on our streets.
"We advise anyone who has been harassed by these individuals to contact the police.
"We will monitor the situation closely and our Imams will be speaking out against such actions."
:: Anyone who feels they may have been a victim or witness is asked to call the incident room on 0207 275 4758, or Crimestoppers, anonymously, on 0800 555 111.