Billionaire investor Ryan Cohen has built a stake in China’s Alibaba Group worth hundreds of millions of dollars and is pushing the e-commerce giant to increase and speed up share buybacks, people familiar with the matter said on Monday. Cohen, who built his fortune by co-founding online pet retailer Chewy Inc and cemented it with investments in videogame retailer GameStop and Apple Inc, reached out to Alibaba last August to express concerns, the people said.