Beijing: Zhang Yiming, the founder of TikTok parent company ByteDance, saw his personal fortune fall by $17 billion last year, according to a new Chinese ranking published Thursday.

The reasons for the losses are unknown, but Zhang is still the second-richest entrepreneur in the world under the age of 40, with wealth valued at $37 billion, according to statistics published by the Chinese firm Hurun.

Ahead of him is Mark Zuckerberg, boss of US tech giant Meta -- the owner of Facebook and Instagram -- whose fortune was estimated by Hurun at $68 billion.

According to the ranking, Zuckerberg also lost money last year to the tune of $8 billion.

Zhang co-founded ByteDance in Beijing in 2012, but resigned from the group in 2021 in the midst of regulatory tightening on China's tech industry.

A Chinese citizen, Zhang is now based in Singapore.

ByteDance's success in China's highly competitive internet sector has been largely thanks to its popular short video app Douyin.

The app is the most valuable start-up globally, with a market capitalisation of $200 billion, according to Hurun.

Its international version, TikTok, is wildly popular with teenagers around the world, but concerns over national security have left its future uncertain in many countries.

Critics say TikTok allows Chinese authorities access to global user data -- allegations the firm has vehemently denied.

Still, the US, Canadian, British and Australian governments, as well as the European Commission, have recently banned their officials from installing TikTok on work phones.

And Washington has threatened the app with a total ban, with TikTok boss Shou Zi Chew hauled before a US congressional hearing recently to defend it.

On Tuesday, TikTok was fined 12.7 million pounds ($15.8 billion) by the British digital regulator over its use of the personal data of children.