Facebook is allowing explicit pornography and gambling websites to reach vulnerable teenagers.
The offensive content shows up in the news feeds of children as young as 13 after they reveal their insecurities online.
They are also shown links to websites selling cannabis seeds, diet pills and dangerous weight loss plans that promote 'purging', 'laxatives' and 'zero calorie' diets.
A Daily Mail investigation found companies and other cynical
users get access to teenagers after they search for certain terms or upload 'posts' – comments, photos, videos, articles and links to other sites – that show they are anxious and vulnerable.
Young Facebook users can even see content from companies selling products that are illegal for under-18s, even when the firm states they are for adults only.
Users are meant to be aged 13 or over, but no proof is asked when signing up to the website. Recent research showed three-quarters of children aged 10-12 in the UK have social media accounts.
In some cases, Facebook is promoting dangerous content to teenagers by suggesting highly unsuitable search terms. The findings will fuel fears that it can be a ‘slippery slope’, introducing curious youngsters to harmful lifestyles.
The Daily Mail set up three fake Facebook accounts – now removed by the firm – posing as teenagers who specifically gave their ages.
The fictional youngsters wrote about feeling insecure and inadequate, and searched for information relating to their worries.
One purported to be a 15-year-old boy suffering depression after splitting up with his girlfriend. The others were girls aged 13 worried about their weight.
Some of the most shocking search results had no obvious connection to the youngsters' worries.
One of the girls was presented with a pornographic video of two people having sex – despite a porn ban on the social network. Facebook has since deleted the video.
The boy did not give any indication he was interested in gambling or drugs. But when he searched 'how can I feel control', he was shown a page promoting slot machines inviting him to play.
When he typed 'want to hide in a hole', he was given a link to an external website with a 'cannabis seed shop'.
The information often looked like adverts, but they were not ‘sponsored’ posts – so no money changed hands between Facebook and those who posted the content.
Instead, canny Facebook users employed hashtags – labels with a ‘#’ sign – and key words to make their posts more likely to appear in search results.
This form of 'guerrilla' advertising is popular with companies, who use Facebook pages to promote their products and services.
The Daily Mail did not find any evidence of Facebook using its algorithm to ensure paying advertisers can target vulnerable teenagers with unsuitable material.
Facebook uses technology to seek out child abuse images and terror material.
But it vets other content only after it is flagged up to one of the site’s 4,500 moderators via its reporting system.
On Monday night, MPs called on Facebook to introduce proper age controls and ensure its website is safe for children.
Labour’s Chris Bryant, a former shadow culture secretary, said: "Facebook have hidden behind this idea that they are a blank canvas … that they are not a publisher or a promoter. But that excuse is threadbare now. Whilst Facebook can be a wonderful thing, it can be utterly pernicious and [it] has got to start cleaning up its act."
Christian Matheson, former member of the culture, media and sport committee, said: "Where are the algorithms preventing children from seeing this sort of thing? The danger is that Facebook normalises this sort of content. Because these posts appear on Facebook, they look normal … we can’t allow that to be the case."
Conservative John Whittingdale, former culture secretary, said: "Facebook is so powerful, they need to be continually making sure they are not being exploited for malign purposes."
Labour’s Chi Onwurah, a former shadow culture minister, said Facebook should not rely on users to report harmful content, adding: "It is unacceptable that a company like Facebook, with its billions of profits, is not exercising its duty of care. It is absolutely disgraceful that it is leaving journalists to find this stuff, instead of getting it under control by looking for it themselves."
An NSPCC spokesman said: "It is extremely worrying that content which gives children tips on how to be thin, or leads to gambling sites or porn, is so readily available through a simple search."
"We want Facebook, and other social media companies, to make sure that children under 18 are automatically given safer accounts when they sign up, with default privacy settings and proactive filtering of harmful content."
Yesterday Facebook said it cares ‘deeply’ about its young users and is always working with experts on new tools to help people ‘stay safe’ online.
It insisted it has ‘strict standards’ to stop the promotion of restricted goods and services to under-18s, and that it will remove any pages that are flagged by users for breaking those rules.
A spokesman said: "We’ve designed many of our features to remind young people who they’re sharing with when they post content and to ensure that sensitive information is protected … We recognise that when it comes to safety there is always more we can do and we’ll continue to work hard to live up to the high standards people expect."