Twitter has become the latest social media giant to disclose disappointing user numbers as it reported an annual loss of $221m.
The San Francisco-based company said its measure of "monetisable daily active users" - those who see ads on the platform - rose by six million to 217 million over the last three months of 2021.
That fell short of Wall Street estimates that the total would reach 218.5 million.
Fourth quarter ad revenues of $1.41bn also failed to meet analysts' $1.43bn target and Twitter's forecast for first quarter sales was slightly below par too.
But Twitter cheered investors by announcing a $4bn share buy-back programme, sending shares as much as 8% higher though the gains later evaporated and they ended 2% lower.
The quarterly results are the first since Parag Agrawal took over as chief executive from Twitter's co-founder Jack Dorsey in November.
They follow a disappointing set of numbers from Meta - the owner of Facebook, Instagram and WhatsApp - last week, which prompted Meta's share price to collapse by a quarter.
Those results had revealed the first fall in user numbers in Facebook's 18-year history as well as a squeeze on ad revenues and pressure from social media rivals such as TikTok.
Twitter, with a market value of $30bn, is a relative minnow compared to Meta, which is worth more than $600bn. Meta's Facebook platform has more than 1.9 billion daily users.
But like bigger tech stocks, Twitter has found its share price under pressure recently as investors fret about the prospect of US interest rate hikes that make bets on future returns from growing companies look less attractive.
Twitter's shares have fallen 12% so far this year.
In its latest results, the company said it had made "meaningful progress" towards its goal of reaching 315 million users and $7.5bn in annual revenue by the end of 2023.
It said user growth should accelerate in the US and internationally this year.
Twitter has been pursuing projects such as audio chat rooms and newsletters to attract users and advertisers but analysts had expected faster signs of progress.
It will need to double its growth rate to 12 million users per quarter if it is to achieve its 2023 goal.
Mr Agrawal said: "I see a strong urgency to improve our focus and execution but also a lot of confidence in our strategy and our team."
The plan will apparently involve a big splurge on bonuses.
Stock-based compensation of $630m in 2021 was up from $475m the year before and is expected to climb to $900-925m this year.
Twitter's annual revenue of $5.08bn was 37% up on 2020 and is expected to grow in the "low to mid 20% range" this year.
Its full-year loss for 2021 was tied to a $766m charge resulting from a lawsuit settlement over allegations it had misled investors.