In order for a user to show up on the front end directory, they must be associated with a department in their employment information. To make sure the user is associated with the correct department, you must: 
  1. Go into Core > Users > Edit User Profile Data 
  2.  Enter Last Name of User and click Search
  3.  Click on the User's name
  4.  Under System Information, select Employment
  5. Click Edit 
  6. Select the radio button for Member for the correct Department
  7. Click Save & Exit