Donald Trump isn’t on TikTok.

And he may not need to be, as his allies and surrogates transform it in his favor. The social-media platform, though still regarded as a hub for Democratic voices and liberal causes, has seen an uptick of right-wing, pro-Trump influencers since the last presidential election.

The increase comes as President Biden signed legislation that would force a sale of TikTok by its Chinese owner or would have it banned in the U.S. That law has triggered a backlash from young voters who backed Mr. Biden overwhelmingly in 2020, some of whom are also opposing his administration’s support of Israel’s war in Gaza. An internal analysis within TikTok found nearly twice as many pro-Trump posts as pro-Biden ones on the platform since November: 1.29 million pro-Trump posts versus 651,000 pro-Biden posts.

“If we allow the Democrats and the leftist organizations and leftist influencers to have a monopoly on the content that’s produced on TikTok, we will lose the next generation of Americans,” said C.J. Pearson, a social-media influencer with nearly 149,000 followers on TikTok who co-chairs the Republican National Committee’s youth advisory council.

But TikTok still presents challenges as the former president seeks to regain the White House.

Among the right, TikTok’s reach remains overshadowed by that of other social media platforms. Although a super PAC backing Mr. Trump joined TikTok this month, it remains unclear whether his unpopularity with young voters, who are on the platform in large numbers, will make it difficult for him to find widespread support. And Republican politicians — including Mr. Trump — have largely resisted joining the platform, with many having vocally opposed it.

Mr. Trump didn’t just oppose TikTok: He attempted to ban it several times as president, citing security concerns about the app’s Chinese ownership as young people used it to mobilize against him in 2020. Yet over the last month, TikTok has become part of his message to young people — that they should support him to protect their access to the platform.

“Young people, remember: Crooked Joe Biden is the one that wants to take your TikTok away from you,” Mr. Trump said this month in a video posted to Truth Social, his social media site. “So if you’re young and you’re smart,” he added, “vote for Donald Trump.”