Police are hunting for a man who allegedly touched up a woman before stealing her mobile phone.
The incident took place on the 8.54pm service from Grays to London Fenchurch Street on March 1, just before the train left the station.
Officers said the man inappropriately touched the victim while the train was in the station and grabbed the phone out of her hand after she challenged him.
The suspect is then said to have fled from the train.
British Transport Police (BTP) have been investigating CCTV footage from on the train and in the station.
Detective Constable David Bishop said: “This incident was incredibly upsetting for the victim and we are doing everything we can to find the individual responsible.
“We take all reports of sexual offences very seriously and won’t tolerate any kind of unwanted sexual behaviour on the railway network.
“If you recognise the man pictured, or have any additional information, please get in touch.”
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting LNA/B2 of 18/03/2014.
Alternatively call Crimestoppers anonymously on 0800 555 111.
