I am not endorsing any of these, but here is a list of some select sites that advertise or serve actors in breakdown and other listings. Respond to ads as you would any purchase or action. Do your homework and research its legitimacy. SAG Actors, always check to see if the project is registered with SAG and if it is either signatory or in the signatory process.
Feel free to send any additions, critiques or referrals to firstname.lastname@example.org