The demonstration drew half-a-million people onto the streets of the territory's business district, including hundreds of journalists, media executives as well as ad agency staff.
The protest forced the authorities to introduce amendments to the controversial law; later delaying its tabling before the legislature by six months to allow more time for public consultation.
Sopa chairman Cyril Pereira said: "I am sending out a general circular to all news organisations urging them to analyse and discuss Article 23 and its latest amendments.
"We will also continue to push for a White Paper, which will set out the exact form, words and phrases of the law."
HK4As chairman Jeffrey Yu estimated that up to 800 agency executives joined the huge protest rally.
Yu said that he took part because "without press freedom, there is no economic prosperity". Agencies which took part included O&M, Grey, Leo Burnett, TBWA, FCB, Euro and Bates. News organisations included Sopa, the Foreign Correspondents Club, the Hong Kong Journalist Association and the Press Photographers Association.
