BEIJING (Reuters) -China's market regulator has begun an investigation into suspected anti-competitive practices by KE Holdings, the country's biggest housing broker whose top backer is Tencent Holdings, two people who know of the matter said. The investigation is the latest into China's big so-called "platform" companies that match sellers and buyers, several of which have been accused by regulators of exploiting consumers. KE Holdings, which operates housing platforms Lianjia and Beike in China, was warned last month by the State Administration for Market Regulation (SAMR), along with dozens of internet companies, against any abuse of market dominance and told to conduct self-inspections.