Yes, SEEKER is a Scrabble word!

Letter values in Scrabble US: S 1, E 1, E 1, K 5, E 1, R 1.

Is it a valid word?

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

someone making a search or inquiry
a missile equipped with a device that is attracted toward some kind of emission (heat or light or sound or radio waves)