The popularity of Chinese-owned video-sharing service TikTok continues to grow among young people in the United States.

Experts say the service more than doubled its U.S. user base to 37 million in 2019. TikTok is especially popular with teens and young adults.

Young people in China are using the service during the COVID-19 quarantine to stave off boredom and communicate with friends, according to BBC News.

TikTok lets users create and share short videos, many under 15 seconds. The TikTok app offers sounds, parts of songs and special effects to create a video. Some TikTok-based memes go viral. Videos often include popular songs from well-known artists, and TikTok has even helped launch the careers of new music stars.

TikTok is considered a competitor to video-sharing app Snapchat and Instagram, which is owned by Facebook. Snapchat and Instagram are heavy on photos and videos featuring fashion, pop culture and humor.

Last year, TikTok was only second to WhatsApp in downloads from Apple and Google. Research company Sensor Tower estimates TikTok has been downloaded 1.65 billion times.

Major companies use TikTok to reach young people who use little or no traditional media.

TikTok is “where the Gen Z party is. That's where they're all hanging out," Kory Marchisotto, chief marketer for U.S.-based e.l.f. Cosmetics, told The Associated Press. Generation Z, or Gen Z, refers to people born between 1997 and 2012.

Companies appearing on TikTok generate revenue through advertising. Often, the companies create user “challenges” as part of their ad campaigns. In challenges, users are invited to publish their own videos in which they perform similar dance moves. One campaign by e.l.f. Cosmetics, for example, asked people to wink and move their lips while following a song. TikTok users created 3 million videos that received more than 4 billion views.

Sometimes the challenges go wrong.

The popular "skull breaker challenge" on TikTok shows someone tricked into jumping into the air as two people nearby kick the person's feet out from under him. Two juveniles in New Jersey who carried out the viral online prank are facing assault charges, according to prosecutors in New Jersey. The victim suffered a seizure, a brain injury and concussion, according to the Camden County (N.J.) prosecutor's office.

''While the challenges may seem funny or get views on social media platforms, they can have serious and long-lasting health consequences,'' acting county prosecutor Jill Mayer told the AP.

Nonprofit privacy group Common Sense Media has issued guidance for parents. The group notes on its website that many videos appearing on TikTok include offensive language and sexual subjects. The group urges parents to supervise what their children watch on TikTok and suggests the service is more appropriate for users older than 16.

TikTok’s head of creator partnerships, Kudzi Chikumbu, told the AP the company is working hard to make sure the app is a “safe and positive environment.”

Last year, the company agreed to pay the U.S. government a $5.7 million fine for collecting personal information from children under age 13. Since then, TikTok created a separate part of the app that restricts possibly offensive material. The app requires users to be 13 years old, although it does not confirm users’ ages. TikTok says it does remove what it calls “wrongly created” accounts if they are reported by other users.

While TikTok has continued to grow since its U.S. launch in 2017, it has also received media attention for being the first Chinese-owned social media service to rise to major success in the U.S.

U.S. lawmakers have raised concerns about TikTok’s collection of user data and the possibility that the company could be sharing information with the Chinese government. In addition, the lawmakers said the app presents national security risks and could be used to censor material for users in the U.S.

TikTok has said it does not share information with the Chinese government and denies the app carries national security risks or is used to censor information.

Concern led the U.S. government to launch a national security investigation into TikTok. Also, the U.S. Department of Defense warned last December of security risks linked to the video-sharing service and urged its employees not to use the app. The warning led several military services to ban the use of TikTok on government devices.

Associated Press and Reuters contributed to this report.