Codepen: our favorite place to write code! It's in the cloud, and you can see results in real time, and you can see other users' creations and use their code as a springboard for your creation!
Girls Go Cyberstart This is a national competition that is made up of challenges- a new round starts soon, so find a buddy or 2, and a sponsor, and get started!
FreeCodeCamp: a place online that offers free lessons in learning all kinds of computer languages.
Codecademy: Online tutorials and interactive lessons for learning to code. It is free, but you can get more content if you pay a monthly subscription.
Girls Who Code: Closing the gender gap in technology related industries is the main focus of this group. You can start a club and get support to meet that club's goals.
Project CS Girls: This is a competition for middle school girls, about using technology to solve a social, health, or ecology problem.