Coca-Cola and Starbucks have joined the escalating big-brand boycott of ads on Facebook, amid concerns social media platforms are doing too little to halt the spread of hate speech.

The two enormous brands join 160 companies, including consumer goods giant Unilever, The North Face and Levi Strauss, in pulling advertising from Facebook.

The campaign has also hit Facebook’s bottom line – on Friday, the company’s market value dropped by more than 8 per cent, amounting to about $US72 billion ($A105 billion).

Starbucks said it would pause advertising on all social media platforms as it explored the best ways to help stop the spread of hate speech.

Coca-Cola said it would pause Facebook advertising for a month to “reassess our advertising policies to determine whether revisions are needed”.

“There is no place for racism in the world and there is no place for racism on social media,” Coca-Cola Company chairman and chief James Quincey said.

“We also expect greater accountability and transparency from our social media partners.”

Meanwhile, Starbucks said on Sunday (US time) it would “have discussions internally and with media partners and civil rights organisations to stop the spread of hate speech”.

Starbucks’ social media pause will not include YouTube, which is owned by Alphabet’s Google, a CNBC report said.

Starbucks and Coca-Cola both said that although they had put a temporary halt on ads, they had not joined the Stop Hate For Profit boycott campaign, which kicked off earlier in June.

Launched by advocacy groups including the Anti-Defamation League, the National Association for the Advancement of Coloured People, and the Colour Of Change, the movement calls on advertisers to put pressure on Facebook and its boss Mark Zuckerberg to adopt stricter policies against hate speech and harassment.

On Friday, Mr Zuckerberg said Facebook would do more to tackle hate speech. He said the company would also expand its policies to better protect immigrants, migrants, refugees and asylum seekers from ads that suggesting they are inferior or which express contempt for them.

“We already restrict certain types of content in ads that we allow in regular posts, but we want to do more to prohibit the kind of divisive and inflammatory language that has been used to sow discord,” he said.

“Today we’re prohibiting a wider category of hateful content in ads.”

The campaign follows  Facebook’s refusal to act on posts from US President Donald Trump, following the killing of unarmed black man George Floyd at the hands of Minneapolis police, and the subsequent worldwide protests.

In May, Twitter put a fact-check on notice on two of Mr Trump’s tweets, prompting a furious response from the President. But Mr Zuckerberg refused to take any action, telling Fox News that Facebook should step away from regulating online speech.

That led to a virtual walkout of Facebook staff, and condemnation from a group of early employees.

-with AAP