Fast-rising ByteDance owns Toutiao, China’s most popular news app with more than 700 million users; it also bought short-video app Musical.ly for $1 billion last year and used it to revamp its own version, Tik Tok, which became the world’s most downloaded nongaming iPhone app in the first quarter of 2018. Next up: Zhang is said to be mulling a Hong Kong IPO that could value the company, which has had a private-market valuation of $20 billion, at more than $45 billion.