While Twitter Inc.’s ad revenue grew 109% year over year in the third quarter, the social network is struggling to add new users and to keep its existing members using the platform.

That’s posing a challenge for Twitter, which aims to “build the largest audience in the world,” said Dick Costolo, Twitter’s CEO, yesterday during a conference call with analysts. Twitter has 284 million active users in the third quarter, up 22.4% from 232 million a year earlier. But during the third quarter it only added 13 million new users, fewer net new users than it attracted in either the first or second quarters.

Moreover, Twitter’s timeline views, a measure of how often its users look at their Twitter feeds, fell 7% worldwide compared to the same period a year ago and 6% in the United States. Anthony Noto, Twitter’s chief financial officer, suggested that some of the international decline was because a year ago users in India were checking the platform for election news and South Koreans were regularly checking it for news related to tensions with North Korea. He didn’t offer an explanation for the decline among U.S. users.

To drive more usage, the social network recently began tweaking the timeline by putting tweets in users’ timelines from people and brands that they don’t follow.

And to bolster its revenue, Twitter has also been aggressively adding new advertising tools, such as testing Promoted Video ads, which let a marketer pay to increase the prominence of a post containing a video. The microblogging site also launched into e-commerce by letting retailers add the Buy button to their tweets.

To reach its goal of becoming a global platform, Costolo says Twitter has a lot of work to do. “I am happy with the strategy and the quality of the work we’re doing, but given our significant aspirations and the breadth of the opportunity in front of us, it’s more critical than ever that we increase our overall pace of execution,” he said.

For the third quarter ended Sept. 30, Twitter reported:

• $320.0 million in ad revenue, up 109.2% from $153.0 million a year earlier.

• Ad revenue of $4.28 per 1,000 views from U.S. users, up 65.9% from $2.58 in 2013.

• Ad revenue of 84 cents per 1,000 views from international users, up 133.3% from 36 cents in 2013.

• $361.3 million in total revenue, up 114.3% from $168.6 million from the same period in 2013. 

• Mobile advertising accounted for roughly 85% of advertising revenue, or roughly $272 million, up from about 81% in the second quarter.

• 284 million monthly active users, up 22.4% from 232 million in the same period a year earlier.

• 227.2 million consumers, 80% of Twitter’s monthly active users, accessed Twitter from a mobile device.

• $175.5 million net loss, up from a $64.4 million loss a year earlier.

For the first three quarters of the year, Twitter reported:

• $816.7 million in ad revenue, up 118.7% from $373.5 million a year earlier.

• $924.0 million in total revenue, up 118.9% from $422.2 million. 

• $452.5 million net loss, up from a $133.7 million loss a year earlier. 

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