How could I be discovered?

It is important that you get involved in programs that will build your talent and give you exposure. There are summer music and theater programs around the country, such as ones at Interlochen and Northwestern. There is also a new summer theater program in New York City called Broadway for All! If I were you, I would spend some time searching on the internet for ways to get involved in more theater and music activities. Additionally, you might consider going to college for music and acting. There are many great schools for that, such as SUNY Purchase, Northwestern, Oberlin, and others.

I agree with the answer above that it is important to get involved in various activities outside school. Whether it's camps, competitions, contests, or even posting videos of yourself on YouTube, get your abilities out there for people to see / discover.