** Hong Kong-listed Meitu 1357.HK slides as much as 13.4% to HK$5.36, lowest since February 17
** Stock last down 7.9%; set for biggest one-day pct drop since October 9, 2024
** Chinese online advertising and internet value-added services provider says substantial shareholder Cai Wensheng disposed 128 mln shares, or 2.81% of issued share capital, between February 17-21
** Meitu's founder and CEO Wu Zeyuan says he is confident with co's business outlook and will further increase his shareholdings when appropriate after the black out period ends on March 18
** Stock up 96% YTD
(Reporting by Donny Kwok)
((donny.kwok@thomsonreuters.com))