Does Chinese have an equivalent to “Person A”?
You would say


  甲、乙、丙、丁……


which come from 天干, you could also say


  路人甲、路人乙、路人丙……


If you know the person's surname, you could also say


  李某、王某……


In case if you want the specify that person's occupation


  某市民、某员工、某政府工作人员……