The feature came about after Martin Lewis, founder of the MoneySavingExpert website, sued over his name and photo being used on fake Facebook adverts.
In return for dropping the legal action, Facebook agreed to donate £3m to set up an anti-scam programme.
That money has been handed over to Citizens Advice to build a new service to help victims of online fraudsters.
The charity has set up a telephone helpline for any type of online scam - not just ones involving fake ads. Face-to-face consultations will even be offered to serious cases - where someone falls into debt or mortgage arrears, for example.
Citizens Advice says it expects to help 20,000 people in the first year of the new service, and warned anyone can be scammed.
There is no typical profile of victims, the charity said, and scams are becoming more and more sophisticated. Some common red flags include:
- something which seems too good to be true - or much cheaper than it should be
- being asked to pay quickly, or in an unusual way - maybe through money transfer or through vouchers
- someone contacting you out of the blue
- being asked for personal information such as a password or Pin
- an advert using celebrity images or endorsements that seem fake or unlikely
Inside Facebook, a specially-trained team has been set up to investigate adverts reported through the new tool.
From Tuesday, Facebook users in the UK should be able to click the three dots in the top corner of every advert to see more options. On top of the usual ones, there will now be the option to "send a detailed scam report" after choosing to "report ad" and selecting "misleading or scam ad" as the reason.
If you or someone you know has been scammed, Citizens Advice recommends you:
- immediately tell your bank if your financial information might have been stolen
- reset your passwords
- update your anti-virus software
- report the scam to Action Fraud
- contact the Citizens Advice Scams Action service on 0300 330 3003 or through the live online chat facility on its website.