Twitter to charge for new services

The social networking site's co- founder Biz Stone tells Jonathan Fildes that Twitter will offer commercial services this year.

A memo leaked from the company earlier this year suggested that the firm wanted to reach a billion users by 2013.

Despite this growth, critics of the firm have questioned its ability to make money.

Earlier this year it secured $100m (£62m), which would value the firm at $1bn. However, it is still to make a profit.