Twitter shares fall amid concern over falling user numbers

Company reports 321 million active monthly users in fourth quarter, a drop of 5 million

Twitter's share price fell close to 10% in on Thursday as record fourth-quarter revenues and the milestone of achieving its first full year of profitability failed to allay investors' concerns over a drop in user numbers and a weak revenue forecast.

The social media company reported 321 million monthly active users in the fourth quarter, a decrease of 9 million year-on-year and 5 million lower than the previous quarter.