There is a pleasure in the pathless woods, There is a rapture on the lonely shore, There is society where none intrudes, By the deep Sea, and music in its roar: I love not Man the less, but Nature more.- An excerpt from Childe Harold’s Pilgrimage by Lord Byron.
I'm not an expert but these are some basic things that I know...Firstly, you need to identify the reason behind your low self esteem because mostly people don't even know what's affecting their self esteem. Secondly, learn to accept your flaws and always remeber that nobody's perfect. Try to avoid negativity; negative thoughts, negative people, just avoid them as much as you can. Thirdly, stop thinking about other people, it's your life not theirs. Lastly, LOVE YOURSELF.
On a more serious note, just focus more on your religion, kids. I feel like these days everyone (not just teenagers but people in general) is so materialistic and involved in worldly pleasures that we forget that this world is temporary...so realize this before it's too late. P.s this is just my opinion...I could be wrong.