(2nd LD) S. Koreans hold massive anti-Park rally for 8th weekend

(ATTN: ADDS new info in paras 10, 14-19)

SEOUL, Dec. 17 (Yonhap) -- Hundreds of thousands of South Koreans held a massive rally in central Seoul on Saturday to call for scandal-hit President Park Geun-hye to immediately step down and the Constitutiona