Before Elon Musk bought Twitter, slurs against Black Americans showed up on the social media service an average of 1,282 times a day. After the billionaire became Twitter’s owner, they jumped to 3,876 times a day.

Slurs against gay men appeared on Twitter 2,506 times a day on average before Mr. Musk took over. Afterward, their use rose to 3,964 times a day.

And antisemitic posts referring to Jews or Judaism soared more than 61 percent in the two weeks after Mr. Musk acquired the site.

These findings — from the Center for Countering Digital Hate, the Anti-Defamation League and other groups that study online platforms — provide the most comprehensive picture to date of how conversations on Twitter have changed since Mr. Musk completed his $44 billion deal for the company in late October. While the numbers are relatively small, researchers said the increases were atypically high.

The World Cup has historically been a boon for Twitter, bringing in record traffic and an influx of advertising dollars.

But this time, when the global soccer tournament started on Nov. 20, Twitter’s U.S. ad revenue was running at 80 percent below internal expectations for that week, three people with knowledge of the figures said.

In tandem, Twitter was rapidly cutting its revenue projections. The company previously forecast that it would generate $1.4 billion in the last three months of the year, down from $1.6 billion a year ago because of the global economic downturn. But as Twitter kept missing its weekly advertising targets, that number slid to $1.3 billion, then to $1.1 billion, two people said.

The meeting was ostensibly organized for Twitter’s advertisers, with whom Mr. Musk has had a volatile relationship in his short time at the helm. He has swung from conciliatory meetings with Madison Avenue executives to threats to put them through a “thermonuclear name & shame” as some brands paused their spending on Twitter because of fears of how his ownership might change the platform’s content.

Civil rights groups including GLAAD and the Anti-Defamation League held a conference call on Friday urging other companies to abandon Twitter, saying that mass layoffs there were gutting what they described as an already anemic content moderation staff.

Even Mr. Musk acknowledged the advertising slump, tweeting on Friday morning that Twitter “has had a massive drop in revenue,” which he blamed on activist groups pressuring advertisers.

More than 40 civil rights groups also sent an open letter to 20 of Twitter’s top advertisers on Tuesday, urging them to suspend their advertising on Twitter if Mr. Musk throws out the platform’s content moderation safeguards. The letter, organized by groups such as Free Press and Media Matters for America and signed by organizations such as GLAAD and the N.A.A.C.P., was sent to top executives at companies such as Amazon, CBS, Coca-Cola, Disney, Mondelez and Procter & Gamble.