Ok for starters, do you need to lose weight? A lot of teens think they need to lose weight or 'tone up' but all they need to do is gain confidence!
First off, learn to love yourself. Not the cocky, self-righteous 'I'm better than everyone else' love but more like being content and satisfied with what you have. Smile. This is the best way to start. Do things you love, with people you love. Surround yourself with people that make you a better person and make you feel happy. Be outgoing and talk to new people at every opportunity. Act confident, even if you don't feel confident. Soon enough you'll feel confident! I can't really give you more advice on that, you have to discover it yourself but once you do you can move on to the next step!
Ok as for weight loss...
Don't fad diet or starve yourself or anything silly like that. Long term effects are non existent when it comes to these methods.
I'm going to tell you what everyone else will say... Healthy eating, excersize and sleep. That's the only way to do it girl!!
I hope this helped and your feedback would be greatly appreciated!