He said police would like to hear from anyone who had seen McGrath's blue 1994 Subaru station wagon in Christchurch over the weekend of May 21 to the May 23, seen McGrath during that time and anyone who he had completed building work for during that time.
Police would continue to maintain a visible presence in the Christchurch suburb of Halswell while enquiries continue, Sweeney said.
Contact Christchurch Police on 03 363 7400 or Crimestoppers on 0800 555 111 if you have information about McGrath.
Cops quiet on missing man
Police are remaining tight-lipped over their investigation into the out-of-character disappearance.
Police started knocking his neighbours' doors last Thursday and remain in the area today.
Approached for an update into the probe today, a police spokeswoman would only say: "The missing person investigation continues. No further updates at this stage."
His brother Simon says although there will "obviously going to be all sorts of theories" about the disappearance, the family is focusing on any sightings of him or his blue 1994 Subaru Legacy station wagon.
In a Facebook plea for information, Simon said: "Very unlike him to go walking - has never done so before and he has been in good spirits."
He also wrote that the family was "up and down".
"At this stage, all we can mainly do is hope."
Simon McGrath referred other inquiries to police.
Detective Inspector Darryl Sweeney, who is leading the investigation, said police "have concerns for his welfare".
It remains a missing persons investigation, police say.
Missing person posters have been placed around the area.
On Friday, police cordoned off his well-kept red brick property where he lived alone.
It remains taped off. Today, a large blue police tent in the front yard had been removed.
White-boilersuited officers have been seen coming and going from the property.
A large police mobile base truck is parked out front.
Halogen lights are in the driveway and locals say there has been a lot of police activity over the past four days.
One neighbour said police came to her last Thursday wanting to eliminate her silver car from their inquiries.
"It's really strange. It has us all worried," she said.
McGrath's blue station wagon was taken away from his property - just a few doors down from where "Black Widow" Helen Milner fatally poisoned Phil Nisbet in May 2009 - at the weekend.
Now, Sweeney is appealing for sightings of the Subaru over the weekend of May 20-22 in the Halswell area.
Neighbours have described McGrath as a quiet man who rarely had visitors.
"We hardly see him," one neighbour said.
"My kids say 'hi' to him when he's out gardening and when he was out biking, which he did a lot."
She said everyone was "really worried", especially at the mounting police activity.
A local shopkeeper said McGrath came in occasionally - but again said he was a very quiet, solitary figure.
She also had concerns for his welfare.
"It's just fingers crossed really," she said.
Anyone who has information about McGrath or has employed him in the past few weeks is asked to call Christchurch police on (03) 363 7400 and cite file number 170523/6008.
Information can also be provided anonymously by calling Crimestoppers on 0800 555 111.
