The head of Instagram responded Tuesday to a growing call from users, including Kylie Jenner and Kim Kardashian, to stop introducing features that make the platform more like video-centric TikTok.

Instagram’s head, Adam Mosseri, said in a video that the social-media platform was shifting toward videos while it attempts to stay committed to creators, to support photos and to put friends’ content at the top of a user’s feed.

Instagram has rewarded users recently who post more short videos, including Reels, which mimic TikTok’s video interface. The platform has also updated its algorithm to give priority to Reels instead of posts from people whom a user follows.

“I need to be honest. I do believe that more of Instagram is going to become video over time,” Mr. Mosseri said.

“This is a lot of change all at once,” he added. “But we’re also going to need to evolve because the world is changing quickly and we’re going to have to change along with it.”

Some younger people have shifted to TikTok and away from platforms owned by Meta Platforms Inc., including Instagram and Facebook, because TikTok features short videos that capture their attention. TikTok’s competitors have invested in copycat designs in recent years that give priority to videos.

“I also want to be clear: it isn’t yet good,” Mr. Mosseri said of the changes Instagram is rolling out. “We’re going to have to get it to a good place if we’re going to ship it to the rest of Instagram,” he said.

His video came days after an Instagram user called Illumitati posted an image that said “Make Instagram Instagram again.” The post had more than 1.6 million likes as of Tuesday morning.

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“Stop trying to be TikTok,” the post said. “I just want to see cute photos of my friends.”

A petition urging the platform to stop mimicking TikTok, saying that the platform was forcing creators to make content that served a new algorithm, had more than 136,000 signatures online as of Tuesday.

Ms. Jenner and Ms. Kardashian, two of the most followed people on Instagram, reposted the image on Monday.

“PLEASEEEEEEE,” Ms. Jenner, who has 360 million followers, wrote alongside the post.

Ms. Kardashian later shared the post with her 326 million followers, adding, “PRETTY PLEASE.”

Ms. Jenner, 24, and Ms. Kardashian, 41, are the third- and seventh-most followed users on Instagram, according to Social Blade, a website that tracks follower counts. The sisters have built business empires in part by advertising their products directly to their followers on the platform.

That kind of influence gives them the power to sway markets, as Ms. Jenner did in 2018 when she said on Twitter that she didn’t use Snapchat anymore. Snap Inc.’s shares fell 6.1% after that, erasing $1.3 billion in market value in one day.

Meta’s shares slid 1.5% on Monday after Ms. Jenner and Ms. Kardashian shared their posts, outpacing the decline in the tech-heavy Nasdaq Composite Index.

The stock fell another 2% Tuesday morning. 

Write to Alyssa Lukpat at alyssa.lukpat@wsj.com