If you move the server from one computer to another, you need to move the index as well. Alternatively, you can re-build the index on the new server (this is the default option when you add a location). If the rebuild index operation takes too long and you would prefer to move the old index, simply copy the folder called
searchindex from the old server installation folder to the new server.
The status of the index server can be seen in the User Statistics pane found in the Status and Management tab page showing information on where the index server resides and the number of locations currently being serviced.