How can I start building my network in the technology industry if I'm only in high school?

The resources and opportunities available to you online today are immense. There are many open-source projects available where you can learn, practice, and prove your skills. You will connect with people in the field who also work on these projects, even if you never meet them in person. Find a project that is interesting but fairly limited in scope; that makes it easier for you to get your head wrapped about the project.

Also, look for hands-on volunteer opportunities with non-profit organizations that deal with technology. Or, sometimes you'll find a non-profit organization that doesn't deal with technology but needs help. In either case, seek out someone who already deals a bit with the technology and can act as a mentor, connecting you with others in the field.

(I could give some more specific advice if you could list some specific areas of technology in which you're most interested.)

Now, I'll tell you how I got started. When I was in high school, I started hanging out in the computer lab, showing the teachers that I was willing to take initiative to get things done. I shared my ideas for improving the computer lab, asked how I could help, showed them what I could do. After a semester of volunteering in the computer lab, my high school gave me a gift of about $200, and connected me with the electronics repair team in my school district where I got my first summer job, working on all sorts of electronics. It was in this role that I found my first mentors in technology and began learning about the Internet.

Take the initiative to learn and demonstrate what you can, and others will become impressed by your knowledge and initiative. But remember that more important than any knowledge is your curiosity to learn and grow your knowledge.

These are all great answers, I would also add linked in even though your still in high school start connecting with people in the industry and related groups and throw in comments where you can. Your network work of professional people will grow and as you look for internships and jobs in that field you will already have a list of connections to reach out to.

Networking is all about getting out there and meeting people. Rodney's advice is solid, resources available online are great.

There is something to be said about just putting yourself out there. I think a skill worth learning is just how to meet and introduce yourself to people successfully. Also remember that everyone is connected to everyone else by only 6 people (I think Facebook analyzed this and found it to be less than 5) so remember to always ask your connections for help!

If you want to meet other people in a field in person, you can try searching on http://www.meetup.com/ for meetup groups near you. Your school might also have a club in a related field.

Another option is to find passionate tech people on twitter, follow & chat with them, and maybe make other connections through them.

What has been said already is great advice! I would also look for events that can help you meet people who are in the field of technology you're interested in. Things like hackathons, events, meet ups, and conferences will help you meet people; after that, be proactive and ask for guidance!