SHANGHAI (Reuters) - Tencent Holdings, China's largest Internet firm by market value, has invested in Chinese social-networking-site Kaixin001, to create a joint SNS platform, both firms said in a statement on Monday. Kaixin001 will issue new shares to Tencent for an undisclosed stake in the company. Both firms did not reveal the size of the investment or other financial details. Kaixin001 will still be the largest shareholder after the investment and will continue to operate independently. "Kaixin001's pursuit of user experience and its open attitude makes it a good fit with us. This investment is Tencent's implementation and upgrade of its open platform strategy," said Tencent's President Martin Lau in a statement. Tencent operates China's largest social networking site QZone that competes with Renren Inc <RENN.N>, China's largest instant-messaging tool QQ and a microblogging website Pengyou that competes with Sina Corp's <SINA.O> Weibo product. It is also China's largest online games operator. Tencent said in June it had doubled the size of its investment fund to 10 billion yuan to invest in online games, social games and mobile games. (Reporting by Melanie Lee; Editing by Jacqueline Wong)