Here's what I did to overcome shyness. I did a couple of plays in junior high school, debate and speech in high school, lectored at my very large catholic church in college, and ran a club of 200 people where I regularly had to get up in front of about 50 people at monthly meetings. I coached debate. I went to graduate school and was a TA for labs of about 20 students. I faked it until I made it - people can't tell I'm shy anymore, and in fact, I am much less shy.
So find some activities where you have to FORCE yourself to speak up, and then DO it, no matter how afraid you are. Truth is, most people are terrified of speaking up in groups. I was a high school debate coach - most of those kids of mine were terrified!!
Also do some confidence building things. For me, a HUGE confidence builder was camping out under the stars in Minnesota in January - it was 20 below zero F. I froze my buns off & didn't get a lot of sleep, but hey! I did it! I feel like if I could do that, i could do anything. Competitive extracurriculars are big confidence builders too.
"social anxiety" is a kind of phobia - and there are 2 ways to deal with a phobia - gradual desensitization, where you gradually expose yourself to more and more intense situations, but start off easy, or "flooding" where you jump right in with both feet, which is what I did. It's called exposure therapy. You can only be terrified for an hour or two, then you run out of adrenaline and calm down quite a bit.
All the best to you! You have to screw up your courage and face your fear - that is what a phobia is, when a person avoids the situation or object that they are afraid of. COURAGE - that's the ticket, and then it will get easier as you keep practicing. It's ok to be afraid.