Carol and Dave Matthews erected a two-metre high steel sculpture in the garden of their new home after losing their 22-year-old son Sam in the 2009 fires at their former St Andrews property.

The couple realised the sculpture was missing earlier this week.

Ms Matthews said she and her husband were devastated by the theft, which they believe occurred between 2pm on Tuesday and 8.30am on Wednesday.

"For our family it gave us great comfort because it was the only physical reminder that we had left of Sam's presence," Ms Matthews told ABC Radio on Thursday.

"For us it is so much more than just a sculpture...I could look at that and think of Sam and not think of the pain that went with what happened on that day. We used to spend a lot of time by the sculpture and it just became part of my recovery program I suppose …

"Now there's just a big hole where it used to be."

Ms Matthews said it would have likely taken at least two people to lift the heavy sculpture and load it into a ute or trailer.

"I'm appealing to anyone who knows where it is to show some compassion and just arrange for it to be dropped off somewhere and let the police know," she said.

"I'm not after anything else other than to get our piece of Sam back."

She said the summer months were still emotionally difficult for Black Saturday survivors.

"It's not just my family that's suffering. This time of the year is very difficult for families that lost so much in 2009 and a lot of us just mentally remove December to March and we go off into our hibernation until autumn comes and the fear passes for another year of bushfire and threat," she said.

"Losing this bit of Sam at this time of the year is just nearly too much to bear."

Anyone with information is asked to contact Crime Stoppers on 1800 333 000.