Twitter had 75 million members at the end of 2009, according to figures from analyst firm RJMetrics.
Many of these accounts are now inactive and the site is not attracting new members at the same rate that it was last summer.
“The number of new users per month is currently at about 6.2 million. This is an enormous number, but it is about 20 per cent lower than the July 2009 peak of 7.8 million,” said Robert Moore of RJMetrics.
“In fact, the past six months have shown steady decline in the number of new account registrations,” he continued.
However, this still equates to more than two new members every second, Moore said.
Around 80 per cent of Twitter members have tweeted fewer than 10 times, Moore claimed, and 25 per cent of accounts have no followers.
So-called ‘power users’ – people who have tweeted more than 3,200 times – represent less than 10 per cent of the 75 million total.
Facebook remains the king of social networks with more than 350 million members.