Top global social media site, Facebook, has announced that it has reached and already surpassed one billion users worldwide.

The news places Facebook well ahead of its rivals in terms of user numbers – with Twitter registering only 140 million users actively accessing the service each month, and Google + notching up just 100 million users on the same monthly basis.

Facebook, which says the important threshold was reached in September, immediately cast a slight cloud over this good news by admitting that the pace of new membership acquisitions was already starting to decelerate, given that so many people around the world – estimated at one in seven – are already members.

The company is also said to be under pressure from shareholders to generate more revenue. Although income for the second quarter of 2012 was reported to be up by $1.18bn (32 per cent) on the preceding quarter, this was still the poorest quarterly growth performance shown by the company since the start of last year.

In an effort to further boost the company’s performance its founder, Mark Zuckerberg, is understood to be looking at developing future growth for Facebook use via mobile applications, as well as investigating enhanced use of e-commerce and search applications.

In regard to mobile, Zuckerberg said:

“There’s five billion people in the world who have phones, so we should be able to serve many more people and grow the user base there.”

Facebook says that the number of those accessing Facebook via mobile has already increased from June’s total of 543 million to 600 million today.