They have issued a photo of the 37-year-old who was last seen in Holdenby Road, Spratton, on Monday January 20.
A police spokesman said: "Officers are becoming increasingly concerned about Brendan.
"He was last seen wearing a black baseball cap, black Nike air top, black bottoms and black shoes. He was also wearing blue and black headphones.
"Anyone who has seen him or knows where he is should call Northamptonshire Police on 101."