* Comes amid rising pressure on China tech (Recasts, adds detail): BEIJING (Reuters) - Alibaba Group Holding Ltd’s (BABA.N) billionaire co-founder Jack Ma will announce a succession plan on Monday to hand the reins of his sprawling empire to a new generation of leaders but will remain executive chairman for the time being. Ma will announce the plan on his 54th birthday and the handover strategy will stretch over a significant period of time, the South China Morning Post (SCMP) newspaper reported citing a company spokesman. Ma, who co-founded Alibaba in 1999, stepped down as chief executive in 2013.