Richard Morris, 52, was last seen when he went for a run in the Bentley area at 10.30am on Wednesday, May 6.
His family are understandably concerned for his welfare.
A spokesman for Hampshire Constabulary said: "We’ve been making enquiries but are now turning to you for your help.
"Richard is described as being white, around 6ft tall, with greying hair and a beard. He is also described as having port birth mark on his face.
"He was last seen wearing a blue long sleeved top with a half zip, black shorts, and blue trainers.
"If you see him, or think you may have seen him since 10.30 this morning please call us on 101, quoting reference 627 of today’s date, or 44200160398."