From the Model Mayhem FAQ:

How do I use the casting section?
Model Mayhem is a great place to find work and we have three separate ways you can actively seek out castings and work opportunities. Please be aware of the casting call and notice rules before you post anything!

Start with this view:

Post a Casting Call if you are looking to hire someone for a project.

Post an Availability Notice if you are looking for work local to you.

Post a Travel Notice if you are traveling and are looking for work where you’ll be visiting.