Use the first letter or letters of the persons Last or First name. 
For example to find "Bob Smith" you can use "Smith" for the last name and "B" for the first name to view all the Smith's that have a first name that starts with "B". 

To further narrow your search you can select the department if known otherwise leave the Department dropdown to "--Select All--" to view all matching records.  The results will be sortable by Full Name or Department.