Police are looking for a group of people who assaulted and robbed a man at Waterplace Park in downtown Providence.  Police were called to the Amtrak station on Gaspee Street on Sunday after receiving 911 reports about a robbery.  The victim told officers that he was pushed down the stairs, and four men stole his phone and iPod.  The suspects are described as 18 to 20-years-old.  Anyone with information about the incident is urged to call PPD.