Format:  
FAMILY/SURNAME, initials. (Year of publication – in brackets). Real Name @User name Site. Date and time of post. Available at: URL. [Accessed: followed by date in square brackets]  

Bibliography example:  
Obama, B. (2014). Barack Obama @BarackObama Twitter. 29 January, 2014. 7:14pm. Available at: https://mobile.twitter.com/BarackObama/status/428607084578369537 [Accessed: 28 February 2014].    

In-text citation example: 
Obama (2014) tweeted that business leaders are starting to realise that America is a better place to invest and create jobs instead of China.