I would suggest you start with something practical, useful, and easy to learn. It should be something that runs on multiple platforms, and has a rich and easy to use--and free--IDE (Integrated Development Environment, an application used to write, build, debug, test, and deploy your code), and will help remove some of the learning curve for learning additional languages. The only one that really fits that bill is Java.
I agree with what others have said. At 13 with no programming experience, do not start with C or C++. There are many a college freshman who even when knowing several languages will struggle when first learning C and C++.
Java's syntax is very similar to C and C++, they are probably about 85% similar, but Java has removed a lot of the syntax that confuses novice developers and causes many errors. And after you learn Java well, learning C++ or C# will be easier and learning C will be mostly easier. If you decide you like coding and want to make a career out of it, you will inevitably have to learn C++ or C. Furthermore, Java will expose you to object oriented programming, something that is very important if you decide to major in Computer Science in college and/or get a job as a software developer. The other reason why I suggest learning Java is that it is used everywhere. Pretty much every major Silicon Valley web company uses Java for some or all of their backend server code (Google, LinkedIn, Facebook, and Twitter just to name a few).