For reference:
Source Exchange> LocalOnly the server, the client is currently connected to will be searched.
> Global (Server)All servers from the server list are queried. Each server is asked individually. This puts added stress on all servers asked, use this respectfully.
If local gives you what you want, leave it at that.
> KademliaSearches all the Kademlia network for the given keywords. The eD2k network, i.e. servers are not search with this method. It may take some time until the search results arrive. Should even a popular search expression yield no results then the system's UDP Port is probably blocked by a firewall or router. The "!" character at the search tab created shows the progress of the search.