Tip-offs from the public have led to police raiding houses they hoped might lead to clues in the case of missing Nelson student Leo Lipp-Neighbours.
As the fourth anniversary of the disappearance of Mr Lipp-Neighbours approaches, police last week executed two search warrants on addresses in Marlborough.
A third Marlborough address was searched by consent of the occupants as a result of information received from the public.
But while computers were seized from the address for forensic examination, investigation head Detective Sergeant Mark Kaveney said they did not unearth anything to link the occupants to Mr Lipp-Neighbours, last seen on January 24, 2010.
After an extensive review of the investigation last year, police concluded his disappearance was the result of foul play.
But they are still in the dark as to where Mr Lipp-Neighbours or his distinctive orange Toyota station wagon may be.
Mr Kaveney said police were not giving up hope of finding him.
"We know that someone out there knows something,'' he said.
"I just hope their conscience gets the better of them sooner rather than later and they come forward with that information.''
Anyone with information that may be relevant to Mr Lipp-Neighbours' disappearance should contact Nelson Police on 03 546 3840 or Crimestoppers, anonymously, on 0800 555 111.
A $50,000 Crimestoppers reward remains active.