Social network Facebook has begun deleting fake page “likes”, independent data suggests.

According to Pagedata, many of the site’s most “liked” pages suffered large drops in numbers on Wednesday.

The move follows the social network’s admission that 8.7% of its users are not “real”, many having been set up by spammers who use them to artificially make pages appear more popular.

The issue poses a problem for Facebook as it seeks to expand its targeted advertising service.

Facebook’s shares have slumped from their initial public offering of $38 in May to $20.62 on Thursday.

Facebook has begun deleting fake page likes

In a blog post written in August, Facebook said: “A <<like>> that doesn’t come from someone truly interested in connecting with a page benefits no-one.”

Technology news site The Verge, citing Pagedata‘s statistics, noted that some of the most popular pages on Facebook had suddenly shed significant numbers of users.

The page for Texas HoldEm Poker, one of the site’s most popular, shed 96,317 “likes” on Wednesday – compared with net gains of about 20,000 each day for the previous month.

Other prominent pages also saw a drop in numbers, including those of pop singers Rihanna (-28,275), Eminem (-15,420) and Lady Gaga (-34,326).

Facebook would not confirm that the purge was happening, but could not provide an alternative explanation for the drop in numbers.

Promoting online engagement with brands is a key component of Facebook’s business model, in which it uses key information – such as age, gender and location – to target certain advertisements at specific recipients.

However, this system is increasingly coming under threat from a black market of fake “likes”, sold in bulk in order to falsely boost a brand’s figures.

A simple search brings up a host of websites offering large numbers of Facebook fans or “likes” – as well as followers on Twitter and views on YouTube.