SAUGUS-A 16-year-old Wakefield boy called police Friday reporting he was robbed at knifepoint after exiting an MBTA bus near Riverside Cemetery on Winter Street, police said.Another person on the bus, described as a white male wearing a black coat, allegedly followed the boy into the cemetery where he pulled a knife on him at about 9:40 p.m.The suspect allegedly stole a Dell laptop computer, a cell phone and $25 cash from the victim, police said.Police searched the area after being called but couldn’t locate the suspect.? Dan O’Brien