Growing a beard at as a teenager can be a difficult thing to do. You'll need to be patient as all guys will develop beards at different points in their life. For instance, I didn't really start growing my beard as a teen. It wasn't until my late 20's and early 30's that I started growing a long beard. I know it's not the best answer for when you want to grow a beard really bad, but it's the reality. Trying to do something to accelerate beard growth is not a good idea.
Stick to what you can control and look at your family history for indication as to how your beard will come in. You can also look to see how many thin blonde hairs as a lot of those will convert into terminal hairs which will be the curly beard hair that grows.
Some tips during the process are to:
1) Grow what you go - shave off the areas of your beard which haven't come fully in yet.
2) Don't compare yourself to others - Everyone is different and it's best to embrace your own uniqueness
3) Be patient - your beard will get better with time
4) Don't be drastic - Don't use rogaine, beard plugs or other "unnatural" beard growing techniques