You could also get involved in something that's new. A club, a sport, or just a simple hobby. You can meet a lot of new people that way. I joined a sport my second year of high school, after having to deal with freshmen year with no friends, and I met such great people. Once shy, I am now very open to them and they are all so kind. You have to take yourself out there in order to meet some fantastic people! Good luck!
Hang out with the friends that you do have PLUS their friends at the same time. You know you have mutual interests already if you hang out with the same people, plus you can ask your current friends to help you out.