$string = "Ajay Devgn Vijay Salgaonkar Shriya Saran Nandini Salgaonkar Tabu Meera Deshmukh Rajat Kapoor Mahesh Deshmukh Ishita Dutta Anju Salgaonkar Prasanna Ketkar Sr. PI Shrikant Prabhu Prathamesh Parab";

preg_match_all('/(\S+\s+\S+)|(\S+)/is', $string, $matcehs); 
shuffle($matcehs[0]);
echo implode(", ",$matcehs[0]);