A memorial erected by a Victorian family who lost their son in the devastating Black Saturday bushfires has been stolen from their home.

Carol and David Matthews's 22-year-old son Sam died when the 2009 fire engulfed their St Andrews home.

The family moved to Plenty, in Melbourne's outer north-east, and built a new home.

In 2011 they created "Sam's Spot" on the acre property, which included a pergola and a two-metre steel sculpture in the centre.

"For our family it gave us great comfort because it was the only physical reminder of Sam's presence," she said.

"I liken it to being able to visit his headstone, as it gave us some relief from the pain that we still feel, and we stood by it and remembered the good times that we had with Sam.

"Black Saturday took away all the physical reminders that we ever had."

Ms Matthews said when the family was ready, they planned to put Sam's ashes in the base of the artwork.

But earlier this week the couple discovered it had been stolen.

"My husband is recovering from a hip operation and that's been occupying our minds and so I'm not sure whether the sculpture was taken on Tuesday afternoon when I was driving him to physio," she said.

"When we got back it was very windy that day, and I had noticed one of the pots had fallen over and broken ... but we didn't automatically go 'where's Sam's memorial?'.

"On Wednesday when I was taking my husband for a surgical check-up he immediately said 'Sam's memorial's gone' and we just stood there looking and looking thinking it must be somewhere.

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

Ms Matthews said this time of year was particularity difficult for those caught up in Black Saturday as the bushfire season approached.

"A lot of us just remove from December to March and we just go off into a hibernation until Autumn comes and the fear passes for another year," she said.

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

Mother appeals for thief to show compassion

Ms Matthews said it was a distinctive piece of art and would be difficult to sell on websites such as Facebook and Gumtree, and thought it may have been taken for someone's private use.

"It's not something that could be taken away easily, it would have taken at least two people to lift it," she told 774 ABC Melbourne.

"It would have to have been loaded onto a trailer or a ute. We had it attached to a concrete base."

She said it would never had occured to them that someone would take it, and many people in the local community understood its meaning.

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

"I'm not after anything else except to get our bit of Sam back."

Senior Sergeant Wayne Spence from Victoria Police said investigators were keen to get the memorial back to the Matthews family.

"If that can be done and it's left somewhere and a phone call is made to police or Crime Stoppers and we'll get that property back," he said.

"That's our focus at this point.

"It's never easy to lose something of this nature, but being so close to the fire season obviously brings it all back."

Senior Sergeant Spence said there were number of road work crews in the area and hoped they may have seen something.

"The property is also up for sale, so we'll be speaking to the real estate agent about prospective buyers who may have visited," he said.

Ms Matthews said the family bought the sculpture so they could have a reminder of Sam with them.

"I was on a trip to Daylesford and I'd seen in an art gallery this beautiful sculpture that was just free form and it felt like a phoenix," she said.

"I just thought I could look at it and think of Sam and not think of the pain that went with what happened on that day.

"We spent a lot of time by that sculpture and it just became part of my recovery, I suppose."