Since Tanaka's early years, he was interested in changes in society by informatization and the field of information-communication. When Yoshikazu Tanaka was working at Rakuten, he used to observe the trends in the Internet space outside Japan. In 2003, when Friendster was launched, it received 3 million users within the first few months. He was surprised by the success that Friendster got in such a short period of time. Realizing the immense growth potential of a social network, he was motivated to start a company in the space. He decided to build a social network service for Japan.
At mere 26 years of age, Tanaka started developing SNS GREE as a hobby. It was 2003, and Tanaka was still working at Rakuten. He started building the first version of GREE in his apartment. Yoshikazu Tanaka made the website open to public in February 2004. Within a month, the website had 10,000 users; and by October 2004, the number of users had increased to more than 100,000.
He needed more people in his team to handle the growing user base. In December 2004, he left his job at Rakuten and established GREE Inc. The company was listed on the one of the Tokyo's Stock Exchange, closing at the highest market value of shares on the first day. In 2010, Yoshikazu Tanaka was ranked as “Asia's Youngest Self-Made Billionaire” under the age of 35 and was selected as the “World's Second-Youngest Self-Made Billionaire” by Forbes.