How do I make friends in USA?

Hi, I'm a 14 year old boy from Norway and I would say my looks are average and I'm in USA now. I'm in San Francisco, I'll be staying here untill sunday and then I leave to Los angeles, and palm springs and Las Vegas after that. I live at a hotel in Powell street, and it's malls and stores everywhere so I guess it would be great places to make friends. But I just don't know how to approach them. I'm going to try to make a female friend, but any tips how to approach? And most girls are in a group which makes it harder, So really need some help here.