What makes video app TikTok such a runaway success?

TikTok has gone viral. Millions of bored people trapped at home are hooked on the video app for the latest dance moves and more.

Owner ByteDance is getting a gold mine of user data and a bigger audience for a follow-up hit. But the unprecedented global success for a Chinese start-up comes with uncharted risks.

ByteDance's first big hit was news aggregator Toutiao, which became a magnet for advertisers in China.

But the real success story is TikTok, the social network that lets users share short video clips of themselves singing, dancing and goofing around.

The app has been downloaded roughly 2 billion times, according to research outfit Sensor Tower - a level of global success even Chinese tech titans Alibaba and Tencent haven't achieved.

The Beijing-based company founded by Zhang Yiming is now the world's most valuable start-up, after backers including SoftBank invested at a US$75 billion (S$106 billion) valuation two years ago.

Quarantines and lockdowns have made TikTok's global appeal all the more lasting.

Canadian rapper Drake's latest dance challenge has racked up nearly 70 million videos in a week; even Jane Fonda, now 82 years old, is posting new workout clips.

In February, it was the world's most popular non-game app, with downloads nearly doubling year-on-year to a record 113 million, according to SensorTower.

It has 800 million monthly active users.

ByteDance isn't immune to the Covid-19 pandemic. It makes most of its money from advertising, which typically gets cut in a downturn.

But a huge trove of user data will at the very least help the company understand what makes non-Chinese netizens tick.

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ByteDance has more than 20 apps and is already mulling its next global hit. New ventures include music streaming, video games, office-collaboration tools, online education and more.

But with greater success comes greater scrutiny. The US government has launched a probe into TikTok's data collection practices, Reuters reported in November.

The company has defended itself by saying data is stored locally and denies allegations it censors content Beijing dislikes.

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