This CCTV image shows a man police want to question after at least four sex workers were robbed at knifepoint in the past four weeks in Westminster, Newham and Kensington.
There were at least four knife-point robberies in the last month in Westminster, Newham and Kensington.
A man arranges to meet women through escort agencies and then produces a knife and steals cash and mobile phones.
Police are advising women who work in the sex trade to be vigilant at all times.
Detectives say the Asian man is aged about 25 to 30 and has a distinctive face with large ears and sunken eyes.
Detective Chief Inspector Dave Manning, of Westminster CID, said : “We are concerned that the violence used in the attacks will escalate and someone will get seriously hurt.
“We are working with support groups to ensure the safety of those at risk but we urge anyone who recognises this man to contact us urgently.”
Detectives have identified a man who appears to be aged 25 - 30 years. He is described as Asian with large ears and sunken eyes.
Anyone with information is asked to call police on 101 or call Crimestoppers anonymously on 0800 555 111
