Jan 18 (Reuters) - TikTok buzzed with nervous

anticipation across the U.S. on Saturday as a looming federal

ban threatened to sever access to the Chinese-owned app that has

captivated nearly half of all Americans, powered small

businesses and shaped online culture.

The company said late Friday that it will go dark in the

United States on Sunday unless President Joe Biden's

administration provides assurances to companies like Apple ( AAPL ) and

Google that they will not face enforcement actions when a ban

takes effect.

The ban would be enacted under a law signed by President Joe

Biden in April and mark the first U.S. shutdown of a major

social media app -- with TikTok boasting about 170 million

domestic users and an estimated $20 billion in 2025 revenue.

The platform has until Sunday to cut ties with its

China-based parent ByteDance or shut down its U.S. operation to

resolve concerns it posed a threat to national security.

Supreme Court justices upheld the ban on Friday in a

unanimous decision and a White House statement suggested Biden

would not take any action to save TikTok before the deadline.

Without a decision by Biden to formally invoke a 90-day

delay in the deadline, companies providing services to TikTok or

hosting the app could face legal liability. It is not clear if

TikTok's business partners, including Apple ( AAPL ), Alphabet's

Google and Oracle, will continue doing

business with it before Trump is inaugurated on Monday.

Uncertainty over the app's future had sent users - mostly

made up of younger people - scrambling to alternatives including

China-based RedNote. Rivals Meta and Snap had

also seen their shares rise this month ahead of the ban, as

investors bet on an influx of users and ad dollars.

Marketing firms reliant on TikTok have rushed to prepare

contingency plans this week in what one executive described as a

"hair on fire" moment after months of conventional wisdom saying

that a solution would materialize to keep the app running.

There have been signs that TikTok could make a comeback

under incoming U.S. President Donald Trump, who wants to pursue

a "political resolution" of the issue and had last month urged

the Supreme Court to pause implementation of the ban.

Trump said on Friday the decision on the future of the

TikTok app will be up to him, but he did not provide any detail

about what steps he would take. Media reports have said that he

was considering an executive order that would suspend the

enforcement of the TikTok sale-or-ban law for 60 to 90 days.

TikTok CEO Shou Zi Chew plans to attend the U.S.

presidential inauguration on Jan. 20 and sit among high-profile

guests invited by Trump, a source told Reuters.

Suitors including former Los Angeles Dodgers owner Frank

McCourt have expressed interest in the fast-growing business

that analysts estimate could be worth as much as $50 billion.

Media reports say Beijing has also held talks about selling

TikTok's U.S. operations to billionaire and Trump ally Elon

Musk, though the company has denied that.

Privately held ByteDance is about 60% owned by institutional

investors such as BlackRock and General Atlantic, while its

founders and employees own 20% each. It has more than 7,000

employees in the U.S.