Credit Action says adverts promising cheap loans for people with poor credit ratings are appearing on the site and many break advertising regulations.

In particular, they are promoting two new products - payday loans secured against a salary or logbook loans secured against a car, it says.

The charity has made a complaint to the Office of Fair Trading.

Credit Action says many of the adverts contravene UK credit advertising regulations, usually by failing to give details of interest rates.

It is now advising Facebook users to warn the website about adverts which break the rules.

A charity spokesman said: "Social networking sites, Facebook in particular, have become hugely popular in recent times, and not just with users.

"Lots of credit companies, especially payday and logbook loans companies, are using the medium to advertise their products.

"It is such a popular method because they can target young people with whom the site is so popular."

'Make it clear'

Chairman of Credit Action's board of trustees, Malcolm Hurlston, said that advertising rules "are there for a reason".

He added: "They are there to make it clear to people from the beginning what they are letting themselves in for."

Mr Hurlston also said some adverts do include the rates of APR but only in the frequently asked questions section, and not prominently on the advert, which is what the rules require.

BBC technology correspondent Rory Cellan-Jones says the adverts are being placed at a time when it has become harder to borrow from traditional sources.

Facebook, along with its main rivals Bebo and MySpace, lets users set up personal web pages and communicate with each other.

It has an estimated 50 million members worldwide and figures released earlier this year suggest that it has 8.5 million UK-based users.

Source: news.bbc.co.uk