I am not an expert, but I knit. I think that you can darn a sweater. Find yarns that match your sweater.
1. You weave stitches through the existing stitches, then across the hole. And contiune stitching across the entire hole.
2 you weave stiches , but perpendicular to the stiches you did in first step, continue stiches until you cover the hole.
Be sure to weave the loose yarn on the wrong side.
Sharon, January 2010