Here is a look at what is happening and tips on how you can spot a scam ad:
What has Mr Lewis decided to do?
Yorkshire Post columnist Mr Lewis has decided to issue High Court proceedings in an individual capacity for a campaigning defamation lawsuit against Facebook. He has said he will be seeking exemplary damages, but not for personal gain - any and all money paid out to him will be donated to anti-scam charities.
What's behind his decision?
It is claimed that within the last year, the social media website has published over 50 fake Martin Lewis adverts.
How long is the legal action expected to last?
Mr Lewis has said he has no idea how long it will take, or how successful it will be - but he said he cannot sit back and let scamming happen.
Solicitor Mark Lewis from Seddons law firm is leading the case.
How big a problem are scam ads generally?
UK anti-scams body Action Fraud recently issued a warning about "the growing problem of criminals using the reputation of prominent people in cryptocurrency scams".
It said anyone who thinks they may be a victim of this type of fraud should contact Action Fraud.
So how can I spot a scam ad online?
Mr Lewis has said he does not do adverts.
And general when going online, Action Fraud says you should not just assume something is authentic - professional-looking websites, adverts or social media posts do not indicate that an investment opportunity is genuine. Criminals can exploit the names of well-known brands or people to make their scams appear legitimate.
Always be wary if you are pressured to invest quickly or promised returns that sound too good to be true.
Action Fraud also says you should avoid unsolicited investment offers, especially those over cold calls. If you are thinking about making an investment, consider getting impartial advice from an independent financial adviser - not an adviser from the company, as this may be part of the scam.