People have been warned not to approach a missing man as he could be dangerous.
Jason Wheeler takes daily medication for mental health reasons but does not have it with him.
The 45 year old was last seen in the Aylesbury area at around 9am on March 30.
Investigating officer PC Benjamin Dyke said: “We are concerned about the welfare of Mr Wheeler as he has not been seen for over a week now.
“We ask that members of the public do not approach him as a lack of medication could make him unpredictable, but instead ring the police to make us aware of his whereabouts.”
Mr Wheeler is 5ft 9ins tall, of stocky build, with short brown hair and brown eyes.
He was last seen wearing blue jeans, a black jumper, a black jacket and brown boots.
Anyone with information can contact PC Benjamin Dyke on 101 or Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org