If you don't know what modeling agencies are, don't worry, many people were discovered without knowing the faintest thing about these pursuits, they were simply in the right place at the same time. Modeling agencies can be damned cruel. They will take your money and make you a bunch of promises, claming they have your best interests at heart, then proceed to completely ignore you for months, as you wonder when you will get your first call to play a big role.
If you are an established model, then modeling agencies can be your friend. If they like you they can send you out on tons of auditions and allow you to be seen a long with your fellow agency mates. Modeling agencies have made people's entire lives change just by sending them out on one audition. Everything can rest on that one bit of information that you have.
Is there anything missing from all this? Yes, it's you. Start taking your career more seriously and break out of your dependence on Modeling agencies. You have many resources at your finger-tips. You just need to access them. Modeling agencies have no love for the little guy, the person just starting out. Take this as a sign that you have to work doubly hard, and show all the modeling agencies that ever passed over you that you are a true thespian.