I started on Rebif in October. I started noticing my hair getting thinner and falling out in November. I was getting quite worried. Luckily I had an appointment with my endocrinologist in early December. I know Rebif can affect your thyroid function, but I don't have a thyroid. I had lost a lot of weight (40 pounds over two months) and thought that could be why there was a problem. The blood tests showed that I was hyperthyroidic. (not sure if that is the right word) I got a lower dosage of my thyroid medicine and the hair loss stopped. It was almost immediate. It has since filled back in and looks normal now.
So I don't know if it will help, but get your thyroid levels checked if you are experiencing hair loss. Might be an easy fix like it was for me.