I was gonna ask if you wore tight ponytails/accessories AS I was reading, then saw your edit.
1st: Stop using stuff in your hair that's tight. If you need to put hair up for some reason (shower/bath, sport) find gentler means (caps, large octopus clips, loose braids, looser satin scrunchies).
Eat well. Getting proper nutrition (including adequate protein and nutrients) help the body produce healthy hair.
Use gentle hair handling techniques when washing and styling.
Make sure you check with your parents before taking hair growth supplements--you are underaged and they need to know in case there is a reaction, which is not impossibe, as I had to go to the doctor with an allergic reation to NourishHair and MSM after taking it for my thinning hair,and I"m 50!
You can easily find out what is good for hair in terms of supplements by googling it or reading the threads here, so I won't rehash. But you MUST inform you mom or dad (whoever is your primary health caretaker/monitor), particularly if you have any pre-existing health conditions. That way, if you do have a reaction to something, they are informed and don't freak.
So, just be sensible in hair caretaking, sensible in eating and keeping stress down, take a sensible multivitamin (with parental approval), and since you are young, your hair will fill in.
But hair that got torn out will take time to grow in. Will not happen overnight. But within a month, you'll notice if there is new hair filling in the thinness, and that will reassure you.
Happy hair to you...