The fact that monthly active users shrank by 1 million during the quarter compared to the previous one - and will fall another "mid-single digit millions" in the next quarter - caused many of these trend followers to fly away.
"Investors are overreacting to (monthly active user) trends", BTIG analyst Richard Greenfield said about the share fall.
But the markets were jittery ahead of Friday's report after rival Facebook spooked investors by warning of slowing sales growth in the second half of the year as it focuses on "putting privacy first".
On Friday, Twitter announced second-quarter results, which showed the user numbers declining as it cracked down on bots and spam accounts.
Macquarie Research analysts last week downgraded Twitter shares to "neutral" despite raising their price target for the stock to $42 from $36. Analysts, on average, had expected 340 million monthly active users in the third quarter, according to Thomson Reuters I/B/E/S. The one million loss came from users in the United States, the company said. "This is an identical overreaction that we saw in Q2 past year". It was the company's third profit in a row and the third it has ever posted.
Nonetheless, the newly announced decline in monthly users clearly anxious investors.
The campaign has drawn some complaints from users, especially conservatives who have accused Twitter of singling them out in an effort to limit their free expression.
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Revenue of $710.5 million, up 24 percent and edging out expectations of $696 million.
Twitter said daily active users rose 11 percent from a year ago, without giving a specific figure.
Over the past several months, the company said it's been more aggressively removing accounts that violate its rules.
But just like Facebook, Twitter said it's hitting a limit on how many people it can attract to its service, raising hairy questions about what these services can become.
The company also warned MAUs could go down even more next quarter due to a combination of account removals, GDPR compliance changes, and its decision to not move to paid SMS carrier relationships in certain markets.
In the financial report released Friday, the company acknowledged that "our work sometimes includes the removal of accounts, some of which are included in our metrics", but that getting rid of problematic accounts will make the service more user-friendly, driving future growth.
In the meantime, Twitter's business, heavily dependent on advertising, is hanging in there. Non-GAAP earnings of 17 cents per share were in-line with estimates.
The company increased its capital expenditures forecast for the year to between $450 million and $500 million, from $375 million to $450 million, as it expands and upgrades the computer infrastructure underlying its service.