Kidnapped overnight: Egyptian activists taken from their homes
The statement held the Egyptian authorities and security services fully responsible for the safety of the two men, who are members of the movement's political bureau.
Nabil and Abdel Magid join other forcibly disappeared or arrested members from their group, most notably 6 April General Coordinator Amro Ali.
Ali took over his post succeeding Ahmed Maher, who was detained then imprisoned last year for allegedly breaking the protest law.
Prior to his arrest, the new 6 April General Coordinator had sought to establish an umbrella formation for revolutionary forces against the current regime.
Ali also sought to launch a campaign to work for the release of the scores of activists and prisoners of conscience detained by the regime of Abdel Fattah al-Sisi since he took power.
The 6 April movement grew from a campaign for labour rights in the textile factories in al-Mahalla al-Kubra. Workers had organised a strike on the 6th of April, 2008, to protest about poor wages, poor management and unfair practices.
The Egyptian Commission for Rights and Freedoms (ECRF) issued last week a report documenting 340 cases of enforced disappearance in Egypt between August and November 2015, with a daily average of three cases.
According to testimonies collected by the Cairo-based human rights organization, victims have been subjected to different forms of torture and abuse during their disappearance.