The River Lea is being searched after a van police believe is being used by a missing man was spotted.
Brian Byrne, 58, was last seen at his Hertford home on May 7.
The white van with a Knight Group logo was reported to the police after it was seen in Crownfield, Nazeing, on Wednesday (May 13).
Police have now extended searches to stretches of the River Lea.
Mr Bryne is described as white, around 6ft 5ins, of stocky build, with balding grey hair.
On the day he went missing he was wearing blue jeans, a t-shirt and tanned ankle boots.
Mr Bryne's van was spotted in Nazeing last week.
A Hertford Police spokesman said: "Police are becoming increasingly concerned for his welfare and have now issued details of the van Brian used for work and could be driving.
"The van is a white Vauxhall combo, index YS52 FAF, with Knight Group branding on the side.
"Anyone who sees Brian, or knows of his whereabouts, is asked to contact police."
Anyone with information is asked to contact police on 101.
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