Custom field is not displayed on listing list, as filter

• make sure, you set custom field as searchable, you can check that in admin panel, when editing custom field
  
• custom fields are shown, only for selected categories, to which custom field has been assigned to. Make sure that custom field in question, is assigned to category in which you want to filter. You can check that on edit custom field page in admin panel.
  

You can access list of Custom fields by logging in to admin page and clicking Custom fields in admin menu.