Adil Najam, who blogs at pakistaniat.com, called Shahzad's death "a warning to the nation".
Comments on social networking and micro-blogging websites focussed on allegations that Shahzad was abducted by the Inter-Services Intelligence agency (ISI).
Mohammed Hanif, the author of ''A Case of Exploding Mangoes'', reflected the public feelings in a message on Twitter: "Any journalist here who doesn''t believe that it''s our intelligence agencies?"
Najam wrote on his blog: "Pakistanis have gotten used to feeling unsafe and afraid. Today they are feeling even more unsafe and afraid...Afraid and unsafe is exactly how the butchers who tortured and then murdered Syed Saleem Shahzad want us to feel."
He added, "The message to Pakistanis and not just journalists, but all who may dare to ''speak up'' was equally cold and bloody and brutal."
Shahzad, who was the Pakistan bureau chief of Asia Times Online, went missing on Sunday evening while driving from his home to a TV station in the heart of Islamabad.
His car and body were subsequently found in Punjab province. The body had signs of severe torture.
He went missing just two days after reporting that al-Qaeda attacked a naval airbase in Karachi on May 22 after failed talks with the military to free some naval personnel arrested for links to the terrorist group.