Yes, THONG is a Scrabble word!

Letter values in Scrabble US: T 1, H 4, O 1, N 1, G 2.

Is it a valid word?

THONG is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

leather strip that forms the flexible part of a whip
underpants resembling a G-string; worn by women especially under very tight pants
a thin strip of leather; often used to lash things together
minimal clothing worn by stripteasers; a narrow strip of fabric that covers the pubic area, passes between the thighs, and is supported by a waistband
a backless sandal held to the foot by a thong between the big toe and the second toe

Also: g-string, flip-flop.