A fall in user numbers of public messaging platform, Twitter, sent its shares down 17%.
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.
The company said it expected monthly user numbers to continue to fall in the third quarter.