Both have the description: "In true holiday spirit, we have decided to give away 2000 vouchers to some of our loyal fans!". It includes a thumbnail image of the brands' logos and sends the person to a fraudulent website.
The victim is told to share the link with all of their Facebook friends. Once this has been done, the webpage tells the person they have won a voucher. To claim the voucher, the victim is asked to complete an online survey - but the victim is never given the prize.
The scammers' goal is to drive more traffic towards certain websites with the online surveys because they are awarded a commission for every one completed, every product purchased, or every account compromised.
The scam is also used to spread malware and obtain personal information.
JB Hi-Fi chief executive Terry Smart said it was "very disappointing" their brand was being used to trick people. "It just seems what the scammers do is look for reputable retailers to use as bait for their scam."
Mr Smart told the Herald his company had traced the scammers to a travel company in the Bahamas but couldn't do anything to stop them.
"It's the internet and it's very hard ... if not impossible, to stop these events happening," he said.
A small number of angry people had contacted JB Hi-Fi after being conned by the scam.
"We're not the first company to have this happen to and I'm sure we won't be the last ... all we can do is keep advising people that this is a scam and hopefully that message gets through."
A Westfield spokeswoman said they became aware of the scam late yesterday and were investigating its origin.
Makeup brands MAC, Maybelline and Estee Lauder have also been recently exploited by free-voucher scammers.
The Ministry of Consumer Affairs' Scamwatch service said it was aware of several Facebook scams circulating.
