Fortunately, you've got a few options. Of course places like youtube can be a good place to showcase you talent. My favorite place is TalentPostings for acting jobs, modeling jobs, and casting calls. You also have the option to get discovered by creating your own Talent Profile which gets sent directly to employers and hiring agencies, which is very effective.
You need to first of all think about how much you want to be a actress/ actor and make sure you know you can give it all your time and effort then just audition for thinks like school plays, your local drama group or just something to get you onto a stage its all experience whether your a lead role or second guy from the left it will help you when you go to find a agent which you will need. Agents get sent the roles which film company's need and then they look through there clients and if they think you suit the role they will send you the date time place ect. Then just keep up the good work and you will get discovered. :)
The way I think about it is you never know. You have no idea how badly I want to be famous. So when ever I'm out I'm always singing or doing something to make someone notice me. Stars get discovered in the most random places. Its alla bout being at the right place at the right time
Email an agency or something. Perform. Ask a principle if you can perform with some friends and model if you want. Do anything. But keep in the spotlight. Live, eat, and sleep spotlight. Form a modeling group. Get on America's Top Model. Do everything you can to become one, but always stay in the spotlight. Welcome!
Join an agency. They then find you background work to start off with and if you are any good then they will find you auditions.
I'm in the same position as you, friend. I want to get discovered VERY badly, but the only way to do this is to keep working at what you are doing, and impress some people out there. :)
Go to Explore Talent.com they want more models.