Twitter may not be a public company yet, but it effectively reported third quarter earnings on Tuesday — and the results were mixed.
The social network updated its S-1 filing with the SEC ahead of its upcoming IPO with new numbers through the end of the September quarter. The previous S-1, which was first made public on Oct. 3, included numbers through the end of the June quarter.
See also: How Twitter's Business Compares to Facebook's
The latest numbers show strong year-over-year growth in Twitter's revenue and continued success in monetizing on mobile, but the company's losses are growing steadily while its user numbers are not.
Twitter revealed that it generated $422 million in revenue through the first nine months of the year, or $169 million for the third quarter. That's more than twice the revenue it earned in the same quarter a year earlier and puts Twitter firmly on the path to topping half a billion dollars in revenue for the year.

Perhaps just as important for investors, Twitter now gets more than 70% of its ad revenue from mobile, up from 65% at the end of June. That serves as further validation that Twitter is much better positioned to monetize mobile than Facebook was at the time of its IPO — though Twitter admitted in the previous S-1 filing that advertising revenue per timeline view on mobile still lags behind desktops because the company's promoted products receive "less prominence" on the smaller screens.
Twitter also noted that the amount of ad revenue it generates per timeline view — its preferred metric for showing how it monetizes user engagement — was $0.97, an increase of nearly 50% from the previous year. Likewise, the number of ad engagements on the social network increased by 58% from the previous quarter, continuing a trend of double-digit percentage increases.

Twitter's revenue is growing, but so are its losses. The company's net loss for the first nine months of the year was $133.9 million, a whopping 89% increase from the same period a year earlier. Operating expenses also ballooned to nearly $550 million through September, well above the $394 million through all of 2012.
Beyond that, Twitter says that the number of timeline views per monthly active user — its metric for assessing user engagement on the social network — actually declined slightly from the previous quarter, though the reason given is pretty vague.
"We experienced a 1% decline in timeline views per MAU during the three months ended September 30, 2013 from the three months ended June 30, 2013," the company wrote in the updated S-1, "which we believe was primarily driven by certain product changes we made in the three months ended September 30, 2013 to improve the overall user experience."

Twitter's user growth rate is slowing down, both on a quarter-over-quarter basis and a year-over-year basis.
Twitter had about 232 million monthly active users in the third quarter, up from 218 million in the previous quarter and 167 million in the same quarter a year earlier. To put that another way, Twitter's active user numbers grew by just more than 6% from the previous quarter, compared to a quarterly growth rate of more than 10% a year earlier.
Perhaps the one silver lining for user numbers, though, is that Twitter did experience decent growth in the United States. Twitter now has 53 million monthly active users in the U.S., up from 49 million at the end of the previous quarter. That's the largest quarter-over-quarter growth since the fourth quarter of 2012.
Twitter is expected to go public on Nov. 15 and it intends to list on the New York Stock Exchange with the ticker TWTR.
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