A prominent TikTok account that features young conservatives, called @ConservativeHypeHouse, posted to the platform pointing to seven billion views the hashtag #Trump2020 has received on TikTok, compared with the approximately 900,000 views #Biden2020 has received.

Teenagers across the U.S. also rallied to TikTok's defense, posting videos with the hashtag #SaveTikTok, which has been viewed more than 730 million times. TikTok says it has 100 million users in the U.S.

Others in the White House appealed to the president's skepticism of Facebook and Twitter, arguing that TikTok represented competition for them. Mr. Trump's team described the potential for two victories for the president: blocking the Chinese Communist Party from accessing user data and putting a U.S. company in charge of the app.

"Have an American company like Microsoft take over TikTok," Sen. Lindsey Graham (R., S.C.) tweeted Saturday night. "Win-win. Keeps competition alive and data out of the hands of the Chinese Communist Party."

In addition to Messrs. Mnuchin and Pompeo, White House counsel Pat Cipollone and Matthew Pottinger, the deputy national security adviser, have been involved in trying to broker the deal, White House officials said.

Allies of the president reached out to Microsoft Saturday evening, urging it to post a simple, positive message on Twitter signaling that Microsoft wanted to help keep TikTok alive, and in American hands. These people told the company the president was warming to a deal and urged Microsoft officials to seize the opportunity.

In a statement posted on TikTok Saturday, Vanessa Pappas, TikTok's U.S. general manager, assured users about the future of the platform. "I want to say thank you to the millions of Americans who use TikTok every day," she said. "We're not planning on going anywhere."

--Liza Lin, Aaron Tilley and Julie Steinberg contributed to this article.

Write to Georgia Wells at Georgia.Wells@wsj.com, Michael C. Bender at Mike.Bender@wsj.com, Kate O'Keeffe at kathryn.okeeffe@wsj.com and Cara Lombardo at cara.lombardo@wsj.com