Twitter Inc.’s ad revenue soared nearly 121% year-over-year in the fourth quarter of 2013, but the social network still isn’t profitable.

The social network in the fourth quarter focused on improving the tools it offers advertisers. For example, its Tailored Audiences tool lets marketers retarget consumers. The social network also launched a self-service advertising platform aimed at small and medium-sized businesses in the United Kingdom, Ireland and Canada. That initiative is particularly important because Twitter has yet to generate much advertising revenue from its international user base. 

For the fourth quarter ended Dec. 31, Twitter reported:

• $219.7 million in ad revenue, up 120.8% from $99.5 million a year earlier.
• Ad revenue of $3.80 per 1000 views from U.S. users, up 72.7% from $2.20 in 2012.
• Ad revenue of 60 cents per 1000 views from international users, up 140% from 25 cents in 2012.
• $242.7 million in total revenue, up 116.3% from $112.2 million from the same period in 2012. 
• Mobile advertising accounted for roughly 75% of advertising revenue, or roughly $164.8 million, in the fourth quarter, up from about 70% in the third quarter.
• 241 million monthly active users, up about 30.3% from 185 million in the same period a year earlier.
• 187 million consumers, 77.6% of Twitter’s monthly active users, accessed Twitter from a mobile device, compared with about 140 million consumers, or 75.7% of its monthly active users, in the same period a year earlier.
• $511.5 million net loss, up from a $8.7 million loss a year earlier. Twitter attributes some of that loss to its acquisition of mobile-focused advertising firm MoPub.

For the full year, Twitter reported:

• $664.9 million in total revenue, up 109.8% from $316.9 million in 2012. 
• $594.5 million in advertising revenue, up 120.7% from $269.4 million in the same period a year earlier.
• $645.3 million net loss, up from a $79.4 million loss a year earlier.

Twitter plans to roll out a number of new ad products and targeting tools this year, including offering new ways to foster “in-the-moment” e-commerce transactions, said Dick Costolo, Twitter CEO, today during a conference call with analysts. “We have only scratched the surface of what Twitter can become,” he said.