Twitter said it removed accounts used for disinformation, hate speech and other abuse as the best way to solidify a base of high-quality users who are attractive to advertisers.
Twitter's advertising revenue jumped 29 percent to $650 million in the third quarter from a year earlier, boosted by ad sales on broadcasts from media companies including Live Nation Entertainment, Major League Baseball and Major League Soccer.
That contributed to a similar jump in overall revenue from a year earlier to $758 million.
The company reported adjusted profit of 21 cents per share.
Twitter has deleted millions of suspicious accounts after it and other social media services were used in misinformation campaigns attempting influence voters in the 2016 U.S. presidential race and other elections.
Monthly active users (MAUs) fell to 326 million in the third quarter. Twitter said it expects them to fall below 326 million in the current quarter, missing the average forecast of 333.4 million.
Increases in advertising sales from video suggest the company is succeeding in efforts to generate more cash from each user and investors have been looking for solid evidence that it would lead to sustainable growth in revenue and profits.
Twitter said the number of its daily active users rose by 9 percent year-on-year, weaker than an 11 percent jump in the previous quarter and its slowest growth rate in two years. The company does not disclose the total number of daily users.
Twitter CEO Dorsey said Twitter has a "different dynamic than a typical social network," though he didn't name larger rivals such as Facebook or Instagram. He said people visit Twitter because they are interested in an event or topic such as sports - and the faster Twitter can show this to them, the better.