First you need to realize, sponsors do not care about you unless you can make money for them. They are not going to sponsor you just to advertise on your shirt, they want a staffer that can sell product. You need to make them more money than they spend on you, A LOT more. This is ALL about money, nothing else. A big company does not care about someone who posts about them on facebook, they want a big name that fishes BFL, FLW, or BASS and can get their logos on camera and in front of thousands of people. Anybody could post good things on facebook about a product.
Also you need to realize there will be more to it than just saying good things online and wearing their logos. You will need to go to trade shows, outdoor shows, product demonstrations, free fishing clinics, and various other events. All of this on your dime working for them. I don't mean to be disrespectful but most companies do not want a young kid to represent them at events, thus they have no need for you.
What you need to do at this point in your life is get a good education and do some fishing. In the mean time, shoot for the smaller guys and build yourself a reputation online with videos and reports.
Take all of the English classes you can from now through college. You will need to be very well spoken or sponsors will not even consider you.
You may start asking companies if they have a junior sponsorship program, some do. It is mostly for the young guys who fish youth tournaments and highschool tournaments. But be aware that a handful of free baits, or a $20 gift card is about all you are going to get from them. They do it for "charity" and to get their name out there. Most of them will be dropped like a hot rock as soon as they get out of the junior divisions unless they go directly to BFL, FLW or BASS.
A good example is a local guy here. He DOMINATED the local tournaments for years, won FLW tournaments as a boater and is one of the best fishermen I have ever seen. You think he is fully sponsored? Not even close.