There's a great Australian online store called birdsnest.com.au where you can shop by body shape. It's not designed specifically with teenagers in mind but they do stock labels such as Cooper Street, All About Eve, Sass and Mink Pink. When you click on a body shape it comes up with hundreds of outfits with shoes and accessories that can be purchased separately. Even if you can't afford their brands, you could get some ideas about what suits your shape. You can even shop by occasion, personality and colour. They have a sale on at the moment too.