Five separate incidents have been reported by male passengers on board Central and Victoria line Tube trains between June last year and March 25 this year.
Police are urging anyone who recognises the man in the image to contact them.
Anyone with information can get in touch by sending a text to 61016 or by calling 0800 40 50 40.
Those wishing to pass on information anonymously, can do so via Crimestoppers by calling 0800 555 111.
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