Are you looking for SOCIAL or RELATIONAL interaction? If it's social, you just answered your own question: find a group you're comfortable with, and participate! It might be a 4-H Club, or Explorer Scouts, or a Church fellowship group, or a co-ed athletic team, or something like Speech & Debate, Drama (there are tech as well as performing jobs in any stage production), or Yearbook at your H.S. My daughter's best H.S. friends were in either the Math Club (she has half a dozen trophies from various competitions) or the Tutoring club (and she picked up a little spending money from helping some middle school kids, as well). A lot of community-based "adult" clubs - like Lapidary clubs, African Violet societies, the local Historical Society, Pinochle clubs, etc - will eagerly welcome you as a member and let you interact with people from a wider range of ages and backgrounds. Some of the adults in these clubs have kids your age, and you'll get to meet them if you impress their parents.

If you're looking for RELATIONAL (boy/girl) interaction, it's a bit more difficult. If you're not one of the "cool" kids or part of the "in crowd", consider getting others to watch out on your behalf. Let your aunts, uncles, coaches, Scout leaders, Church youth workers, etc know that you need help meeting compatible people of the opposite sex. Don't choose "just anybody", though - it should be an older person who really knows you and has the best interests of young people at heart. (Your school friends are perhaps the worst choice - they'll just try to hook you up with whoever isn't attached at the moment. Which is probably OK for casual, non-relational activities that just get you out of the house for an evening but unlikely to lead to anything long term.) Adults who are in position to know you often recognize the sort of person you'd be compatible with, and either guide you in a search for that person or even introduce you.

(It worked for me: my first girlfriend lasted about 3 months at the end of H.S. My 2nd wasn't until after I graduated from college. That's lasted 31 years (so far); we were introduced by her aunt, whose husband pastored the church I attended at that time.)