Staff / Staff member / staff members
UsageUse staff for the workforce collectively and staff member when referring to one person. Use staff members when a precise count matters.
Staff
Use when
You mean the employees of an organisation collectively.
Example
“Staff were briefed before the service announcement.”
Staff member / staff members
Use when
You are counting or referring to individual employees.
Example
“Three staff members will support the event.”
Quick check
a staff, each staff, every staff, three staffs
Usage note
Staffs can be correct when referring to separate groups of employees, such as the staffs of two agencies. It is usually not the plural for individual employees.