Avoid automatically resorting to friends and family. As a last resort, fine, but exhaust all other possibilities first.
Look up local casting agencies and make your pitch. Some charge, others don't. Let them explain their modus operandi. If no fit can be found, move to Step 3.
Post on websites like Craigslist and Mandy. Though they may seem "cheesy," you would be surprised how many legit people probe these sites.
Visit local playhouses and speak to the directors. Not only are theatre actors experienced with the craft, but they may also be looking for that big film break.
There are specific websites out there filled with actor auditions on tape, allowing you to streamline the process. These sites have actor profiles discussing whether or not they are willing to work for free.
Watch other low budget indie films and contact actors from those films. They are already predisposed to the process and may enjoy the experience.