Relatives of Cherif Diallo, who works for a private channel, think he may have been kidnapped.
Hadja Salimatou Diallo, the journalist's aunt, told AFP: "I appeal to all those with good will, to all those who might have information about the kidnapping of my nephew, to share it with us."
Diallo's colleagues at Espace TV last saw him as he left the office on the evening of July 23, news director Moussa Moise Sylla said.
"He was seen by some family members in the early evening... He then went out again for a business meeting," Sylla said.
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Sylla said he was "very worried" about what might have happened next.
Conakry's chief of security Aboubacar Kasse told AFP an investigation was underway, adding: "We do not yet have any reliable leads."
Guinea was ranked 102nd out of 180 countries in the 2014 Reporters Without Borders (RSF) press freedom index.