
It’s been hard for investors and other tech players to put a firm value on one of the fastest-growing area of the consumer internet, social-messaging apps like WhatsApp and Line. In February, Facebook said it was paying $19 billion for WhatsApp, a price many found risibly high. Japanese e-commerce giant Rakuten bought Viber—a similar app— around the same time for $900 million. The other top social messaging apps are either owned by a huge listed parent company such as Tencent or in private hands.

