Gree Inc. extended losses in Tokyo trading a day after founder Yoshikazu Tanaka, Japan's youngest billionaire, lost $702 million as his social-gaming company plunged on concerns one of its sales methods may be illegal.

Japan's second-biggest operator of social games tumbled as much as 16 percent to ¥1,380 and traded at ¥1,561 as of 10:38 a.m. The stock dropped by the ¥500 daily limit Monday, wiping ¥56.1 billion from the value of 35-year-old Tanaka's shareholding, based on calculations by Bloomberg News.

Gree led declines among Japanese social game-related companies after the nation's Consumer Affairs Agency said it's considering whether a sales method called "complete gacha" violates the law. The Yomiuri newspaper said Saturday the agency will ask social-network game operators to stop using the system because it prompts customers to pay excessive fees.