Twitter users launched a hashtag called "Where is Massouny?" to demand the disclosure of the whereabouts of activist Mostafa Massouny.
Massouny has been missing since June 2015.
Massouny's friends accused the Interior Ministry of abducting him.
Human Rights Watch called on Egyptian authorities in July to disclose the whereabouts of dozens of forcibly-disappeared citizens and activists and to either release them or charge them with a recognizable crime.
The Interior Ministry issued a statement denying the accusation and stressed it has investigated Masouny's disappearance.
Edited translation from Al-Masry Al-Youm