A good sonar will be your best friend. If you want to troll you can get a Torpedo Diver which acts like a downrigger with very little drag.
http://www.torpedodivers.com/torpedo.asp
As others have said, jigging spoons or other metal works very well. Depending on the time of day and when they are actively feeding you can find them anywhere under the thermocline. Look for schools on your sonar in > 50ft.