Twitter says the deletion of abusive accounts is responsible for a fall in monthly active users.
Twitter Inc. forecast that revenue in the first quarter would be weaker than expected while full-year operating costs would rise, sending shares down more than 10 per cent in midday trading on Thursday.
Investors' concerns over the weak forecast overshadowed strong fourth-quarter results for the social-media company – including a 24-per-cent jump in total revenue, helped by growth in its video-advertising business.
The number of monthly active users on the social-media platform fell to its lowest point in two years and for a third consecutive quarter. Twitter said it would no longer disclose monthly active users, a statistic internet companies have routinely reported over the past decade, and would instead provide the number of monetizable daily active users.
Operating expenses are expected to surge about 20 per cent year-on-year in 2019, the company said, due to efforts to improve the health of its platform, exceeding analysts' average estimate of 12 per cent.
"The street is just about done giving them a break about it," said J.J. Kinahan, chief market strategist at TD Ameritrade.
Twitter also expects capital expenditure of between US$550-million and US$600-million in 2019, well above analysts' average estimate of US$415-million.
Shares were down more than 10 per cent at US$30.56 in midday trading.
Expected total revenue for the first quarter of 2019 is between US$715-million and US$775-million for the first quarter of 2019. The midpoint of that range was below analysts' average estimate of US$765-million, according to IBES data from Refinitiv.
Monthly active users totalled 321 million in the fourth quarter, in line with analysts' forecasts but down from 330 million a year earlier and 326 million in the third quarter.
While directly comparing the number of daily active users with those of Twitter's peers may be difficult as there is no industry standard on how social-media platforms measure the metric, Snap Inc. reported earlier this week that it had 186 million daily active users in the fourth quarter. Facebook had more than more than a billion in the same period.
"Twitter's pivot to mDAUs [monetizable daily active users] helps ad buyers better understand the potential reach for their advertising," said Aaron Goldman, chief marketing officer at 4C Insights.
Total advertising revenue surged 23 per cent to US$791-million in the fourth quarter, with more than half coming from video ads by corporate clients.
Overall revenue in the fourth quarter rose to US$909-million, handily beating analysts' estimate of US$868.2-million.
Revenue from data licensing and other non-advertising businesses rose 35 per cent from a year earlier to US$117-million.