SAN FRANCISCO (AFP) - Twitter on Thursday reported its revenue nearly doubled in the final three months of last year, but user growth fell short of analyst expectations.

"We closed out the year with our business advancing at a great pace," said Twitter chief executive Dick Costolo.

Revenue hit US$479 million in the fourth quarter, up 97 per cent from US$242.6 million in the same period a year ago.

Its quarterly loss shrank to US$125 million, as compared with a US$511 million loss a year ago.

The number of active monthly users of the San Francisco-based one-to-many messaging service monthly grew to 288 million - just four million more than in the previous quarter.

That figure fell short of expectations - analysts had predicted the figure would climb to 292 million.

About 80 per cent of the people using Twitter monthly connected with the service using mobile devices.

For the full year, Twitter reported a loss of US$578 million, during which revenue more than doubled to US$1.4 billion.

Twitter shares were up more than eight per cent to US$44.96 in after-market trades that followed the release of the earnings figures.

Twitter is stepping up efforts to boost its user base and monetization as the messaging platform faces pressure from lacklustre growth since its stock market splash debut in late 2013.

This week, Twitter unveiled plans to sell ads that run outside its own platform in what could be the start of a broader advertising network.

The plan allows advertisers to place "promoted tweets" on third party sites, the first of which are Yahoo Japan and the news app Flipboard.

In January, Twitter began rolling out new group chat and video features.

According to reports Thursday by Bloomberg News and The New York Times, Twitter has reached a deal with Google to make its short messages more visible on the Internet.

The deal would allow tweets to show up in Google searches as soon as they are posted.

Deutsche Bank analyst Ross Sandler said in a research note this tie-up "could be the catalyst to push shares meaningfully higher," and help Twitter add users.

The research firm Trefis said in a report this week that Twitter has "solid monetization potential" over the long term.

On previous earnings calls, Costolo has pointed out that there are huge ranks of people who visit Twitter to check out posts but do not check in as registered users.

Twitter co-founder Jack Dorsey launched a "tweetstorm" last week defending the company and Costolo.

Dorsey said "there isn't a single person who has been thinking longer about Twitter" than its chief executive.

Dorsey also said Twitter is not just a company but "a movement."

"Twitter has more global awareness than most century-old companies, and yet the brand actually stands for something," he said.

"The Twitter bird has come to stand for empowerment and a positive force in civil society."