New York CNN  — 

More than half of Twitter’s top 1,000 advertisers in September were no longer spending on the platform in the first weeks of January, according to data provided to CNN by digital marketing analysis firm Pathmatics by Sensor Tower, in a striking sign of how far reaching the advertiser exodus has been following Elon Musk’s acquisition of the company.

Some 625 of the top 1,000 Twitter advertisers, including major brands such as Coca-Cola, Unilever, Jeep, Wells Fargo and Merck, had pulled their ad dollars as of January, according to estimates from Pathmatics, based on data running through January 25.

Wells Fargo said it “paused our paid advertising on Twitter” but continues to use it as a social channel to engage with customers. The other brands did not immediately respond to a request for comment.

As a result of the pullback, monthly revenue from Twitter’s top 1,000 advertisers plummeted by more than 60% from October through January 25, from around $127 million to just over $48 million, according to the data.

The data demonstrate the sharp decline of what was once a $4.5 billion advertising business for Twitter. After Musk completed his takeover of the company in late October, advertisers began to worry about the safety and stability of the platform given his plans to cut staff and relax content moderation policies. In early November, Musk said Twitter had seen a “massive revenue drop.”

Although Twitter’s ad business was always much smaller than that of competitors Facebook and Google, it was still responsible for the vast majority of the company’s revenue. Musk must now fill in that gap as he stares down interest payments for the debt he took on to buy Twitter for $44 billion.

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Twitter, which eliminated much of its media relations team during last year’s layoffs, did not immediately respond to a request for comment.

After initially clashing with advertisers, Musk now appears to be trying to woo them back to the platform. The company reportedly offered a Super Bowl “fire sale” deal for advertisers in an attempt to win them back for one of Twitter’s biggest audience days of the year. Twitter has also partnered with a third-party “brand safety” firm that says it can show advertisers if their ads appear alongside inappropriate or unsafe content on Twitter.

But the pushback continues. A coalition of civil society and civil rights groups renewed calls on Thursday for companies to join what they say is more than 500 advertisers who have stopped advertising on Twitter. The latest effort came after a research report from the Center for Countering Digital Hate, a member of the coalition, raised concerns about ads “appearing next to toxic content” from previously banned accounts.

In his first months in charge, Musk rolled back bans on users who had previously violated Twitter’s rules, including former President Donald Trump. He also dissolved a third-party content oversight group and halted enforcement of its Covid-19 misinformation policy.

Some advertisers also complained that the Twitter employees they previously worked with had been terminated by Musk, causing confusion. In November, Musk complained that Twitter had seen a “massive drop in revenue.”

But Musk has stood by those policy changes, and has since been scrambling to reduce costs and find new revenue streams for the company. Those efforts include dramatically cutting staff, revamping its paid subscription service and, more recently, announcing the controversial move to charge researchers and developers reliant on Twitter’s API, which allows third parties to tap into Twitter’s systems.

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For now, however, Twitter remains reliant on advertising revenue as it reportedly struggles to grow its paid subscriber base.

Even among the top advertisers that remain, many have dramatically reduced their ad spending on the platform, according to Pathmatics data. HBO, for example, was Twitter’s top advertiser in September, spending nearly $12 million on ads that month, but for the month of January (as of January 25), it spent just over $54,000. (HBO, which is owned by CNN parent company Warner Bros. Discovery, did not immediately respond to a request for comment.)

A small number of Twitter’s top advertisers spent more on the platform in January than they did the month prior to Musk’s takeover, including ESPN, Salesforce and Apple, the latter of which Musk briefly and publicly feuded with for allegedly threatening to block Twitter from its app store. ESPN, Salesforce and Apple did not immediately respond to a request for comment.

Musk said in a tweet earlier this month that the previous three months had been “extremely tough, as had to save Twitter from bankruptcy,” but that the company “is now trending to breakeven if we keep at it.”