This a two part sweater: from the back it looks like two layers - one longer then the other, and from the front it looks like toi are wearing a strapless haut, retour au début and a sweater on haut, retour au début of it . link
photo
sweater
haut, retour au début
This Teen Fashion photo contains
cardigan.
There might also be
pull-over, débardeur, pull, orage, chandail, cavalier, and pull.