Shares in Facebook continued to slide on Tuesday, after an analyst claimed the dominant social network had seen a modest drop in its userbase.

Capstone Investment's Rory Maher said Mark Zuckerberg's company suffered a 1.1 per cent fall in US users over the last six months. The number of European Facebookers had also declined, he added.

Meanwhile, Facebook's stock hit a month-long low yesterday finishing the day at $28.09 on Nasdaq, after falling some 8 per cent at the start of the week.

Maher's methodology was based on proprietary software his outfit had used to track how many people were accessing Facebook over the past two quarters in more than 200 countries on 500 user pages.

He also spotted that Facebook had hit a wall in terms of trying to build its userbase in the 23 countries where the network had already surpassed 50 per cent of the population.

Only nine of those countries actually exceeded the 50 per cent userbase in the last three months. But the remaining 14 countries either saw minor changes (UK growth was flat, for example) or had fewer signups to Facebook.

The company claims to have around 900 million people worldwide using Facebook. And it has previously said in regulatory filings that it needed to penetrate other markets, such as China, to help generate growth in its userbase.

It has also noted the plateau effect of user growth in its more mature markets.

Either way, Wall Street clearly took umbrage with Facebook yesterday, and as noted by Forbes the company's Q2 earnings report due on 26 July may well be making some investors rather twitchy.

The Register asked Facebook to comment on this story, but it hadn't got back to us by the time of publication. ®