1. To start searching over network you should specify path to search. You can do it in two ways. 

1-a. You can open drop down list "Search in" and then select "My Network Places" to select your network drive

1-b. Use "Search in..." options to specify more drives to search. Remove all paths from current list and then click "Add path" button to add path to your network drive.

What make searching over network more time-efficient read customizing search topic;