The three main weight loss tips for teens is to learn what puts on the weight, learn to give up things that put on the weight and then to put better habits into place.
There are lots of calories in sugared beverages. One 12-ounce soda contains about 150 calories. Drinking three cans of regular soda each day, can add up to about a one pound weight gain each week. If you regularly drink sugared beverages, try cutting back. Start by switching some or all of your consumption to sugar-free drinks. Consider making your own flavored beverage by simply squeezing fresh lemon juice into your water. Gourmets drink water with their meals to bring out the full flavor of foods.
Avoid sugar and sweets made with sugar. Reduce the amount of bread that you eat. (I have seen teenagers that lost a lot of weight by just eliminating white bread)
Avoid foods with excess fat. Try to avoid fried foods. Salad dressings have a lot of fat.
Exercise. Run. Park your car further away and walk. Walk (this also relieves stress.) Play outside games or play sports.