Joseph Smith-Sturgess, 30, was last seen at about 5am on Saturday (25 June) near Hinchingbrooke Hospital.
Officers are becoming increasingly concerned for his welfare.
Joseph is described as 5 foot 10 tall, of slim build and has curly blonde hair.
He was last seen wearing dark clothes and a red baseball hat. He was also carrying a dark rucksack.
DI Juliet Heald said: “Joseph lives in St Neots so may have travelled back towards his home.
“We’re appealing to anyone who has seen him, has information about his whereabouts or who has heard from him to contact us as a matter of urgency”.
Anyone who has seen Joseph or who has information concerning his whereabouts, should call 999 quoting incident 92 of 25 June.
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