SINGAPORE (Reuters) -Asian shares and global stock futures tumbled on Wednesday, led by a heavy decline in technology names and as worries about the global growth outlook drove investors out of risky assets, while oil prices hit multi-month lows. Stock benchmarks in Tokyo and Taipei led the slump in Asia, each falling more than 3%, while MSCI's broadest index of Asia-Pacific shares outside Japan was last 1.8% lower. "Volatility obviously is picking up," said Jason Teh, chief investment officer at Vertium Asset Management.