Actually how you'd say it in Japanese would depend on the context. Maybe I'd say "ありがとうございます/Arigatou-gozaimasu (To thank for the support that's being given or will be given)"/"ありがとうございました/Arigatou-gozaimashita (To thank for the support that was already given)". My dictionary gives "ご助力感謝いたします/Go-joryoku kansha itashimasu" as a translation for "I appreciate your support/help", btw.

ご苦労様でした。 Go-kurou-sama deshita.

Domo 雲小泉 I should be more specific...I appreciate your assistance in Japanese written in English Characters.