Whittaker's has been forced to warn Facebook customers to stay vigilant after a fraudulent ad bearing company branding promised people would be sent free chocolate.

In a Facebook post on Wednesday, the Wellington-based company said it had been made aware of the scam and was working to remove it.

"Caution Chocolate Lovers, we have had a few of you contact us about a scam going around that invites people to become Whittaker's testers," the post said.

"We wanted to alert you all that this is most definitely a scam, and the message is not from here at Whittaker's.

"We are doing what we can legally but stay vigilant out there and we suggest you do not engage with them."