Twitter has posted its weakest quarterly revenue growth since its stock market flotation in 2013, with shares plunging 10% on opening in New York.
The microblogging service, which has never made a profit, reported a 1% rise in fourth-quarter revenue to $717m (£571m).
The figure failed to meet market expectations of $740m for the three-month period.
Twitter said its annual net loss had eased to $457m (£364m) from $521m the year before, despite quarterly losses widening.
It also warned that underlying profitability would take a hit in 2017 because revenue growth would continue to lag user growth amid stiff competition for advertising spending.
Its results statement said: "Advertising revenue growth may be further impacted by escalating competition for digital ad spending and Twitter's re-evaluation of its revenue product feature portfolio, which could result in the de-emphasis of certain product features."
It highlighted its commitment to revenue products that "strengthen our unique value proposition, especially in live and video".
They have included big investments in live streaming of sport, with the aim of making its proposition more attractive to not only users but also advertisers.
It reported a 4% year-on-year jump in average monthly active users to 319 million in the last quarter - two million higher than the figure it had given in the July to September period.
That compares to a total of 1.9 billion Facebook users and more than 500 million on Instagram.
Twitter's chief executive, Jack Dorsey, said: "We overcame the toughest challenge for any consumer service at scale by reversing declining audience trends and re-accelerating usage."
That could be potentially explained by the frenzy over the US election - with President Trump a prolific Twitter user.
Mr Dorsey said he expected growth to continue.
He added: "While revenue growth continues to lag audience growth, we are applying the same focused approach that
drove audience growth to our revenue product portfolio, focusing on our strengths and the real-time nature of our service.
"This will take time, but we're moving fast to show results."
Its weaker underlying profit expectations for 2017 added to the pre-market stampede from its stock by investors as they were more than half the figure Wall Street was expecting, according to a survey of industry analysts by FactSet.
The plunge in its share price leaves the stock 35% down on the offer price set at its flotation in November 2013.
(The sky News)