Hypothyroidism could be a cause among many. In some instances it could be the sole cause. But with your description of social anxiety, other factors may be at play to which hypothyroidism could contribute.
Years ago, I, too, suffered from anxiety and severe panic attacks and I also had a sluggish thyroid. However, my anxiety was not necessarily social anxiety, mine was propelled by fear caused by unresolved emotional issues. So what I am saying is that if there is an emotional component, it must also be addressed. Healing from anxiety and panic is very complex because in many instances it has an emotional and a physical base. And it is a very individual condition. There is basically not a cureall for everyone. However, the supplements I described above are the ones that correct the nutritional imbalance in the body and relieve anxiety.
The best thyroid supplement is iodine. I take SSKI and magnascent daily that I get from Trapper. A great many people are deficient in iodine and they have no clue. Iodine deficiency comes at a cost one way or another. Yet, as you will read from the description of the supplements in my prior post, other nutritional deficiencies come into play. All are important and diet plays a vital role.