Well, it depends on the style and body type of the girl. If it is a skinnier or averaged size girl, or even over average Hollister, Aeropostale, Abercrombie and American Eagle are great but expensive stores. Old Navy has cute clothes that look more adult or proper. And Pacsun is colorful and fun, that anyone could like. But Hot topic is also a good choice for band tees, skinny jeans and jewelry. Or just go to a department store :)
new look, internationalle, peacocks, george,
FashionTiy
zumiez and tillys
Gap and Gymboree are good stores for little girls clothing.
Fast food places generally... and some clothing stores will hire 16 year olds.
Good online clothing stores for teenagers would be a teen based store.us A store that specialises in especially for teen style. Stores such as wetseal, rue 21, forever 21 arsenal stores teenagers would be interested in.
Try sites like eBay or amazon. Some discount stores have good deals. Check for sales at stores. The swapmeet might some times have cheap cute girl clothing.
JC Penny's, Macy's, Target (not fully clothing), WalMart (not fully clothing), Nordstrom, and many other stores.
In the UK the stores Pumpkin Patch and Mothercare specialise in children's clothing, however, one can also find a good selection at Next, Asda, Tesco and Gap.
You can buy many plus size clothing, for low, reasonable prices at Wal-Mart. If you aren't on a budget some good stores may be Kohl's, JCPenny, and Target.
You can find casual clothing just about everywhere. Some popular clothing stores for business casual wear would be JCpenney, Macy's, Ross, and Kohl's. They have a good selection of clothes you are looking for.
garage, Aeropostale, American eagle, hollister, Abercrombie and Fitch, and campuscrew