A fall in user numbers of public messaging platform, Twitter, sent its shares down 18%.
The fall, in pre-market trading, came despite record quarterly profits.
The number of people using Twitter on a monthly basis was down by one million on the previous quarter at 335 million.
During the quarter the company had been actively purging fake accounts that manipulate the platform and Twitter boss Jack Dorsey said the results reflected these changes.
But analysts had predicted Twitter would gain users.
Revenues from advertising rose, delivering Twitter’s third profitable quarter in a row.
“Our second quarter results reflect the work we’re doing to ensure more people get value from Twitter every day,” he said.
“We want people to feel safe freely expressing themselves and have launched new tools to address problem behaviours that distort and distract from the public conversation.”
Tech firms have been under pressure in several countries to be stricter over abusive content and misinformation or “fake news” as well as political influence and protection of personal data.
Twitter recently removed or suspended a number of accounts, which the firm said was one reason behind the fall in monthly users to 335 million in the second quarter. Most of the fall was in the United States.
Mr Dorsey said in a statement that daily users grew 11% compared with a year ago, saying this showed the firm’s measures were turning the service into a daily utility.
Sales, at $711m, were up 24% compared with last year and above analysts estimates. Twitter said it had benefited from ads related to the World Cup football tournament in Russia.
Profit was $100m, marking Twitter’s third quarter in a row of profits. But competition for online advertising is stiff.
This week big tech stocks have been in the spotlight after Amazon was boosted thanks to record results in the second quarter, but Facebook warned of less rosy future growth, which led to a nearly 20% fall in its share price.
Google’s parent company, Alphabet reported stronger than expected ad sales.