The Twitter hashtag "where is Massouny?" has been trending in Egypt for the past three days, referring to former activist Mostafa Massouny, who has been missing for nearly four months.

On Wednesday, the human rights grassroots campaign Freedom for the Brave, which works to release detained political prisoners in Egypt, reported that 26-year-old Massouny disappeared when he went to buy some food on the night of 26 June while staying at a friend's home in downtown Cairo.

Massouny's friends and family say that two weeks into his disappearance, his colleagues informed them that State Security agents had been asking about him at work.

His family alleges that they reached out to someone in State Security who told them that Massouny was in custody and would be released from the State Security headquarters in Cairo's Lazhougli after investigations were concluded. Four months later, his family says they still do not know what happened to him or where he is.

The Freedom for the Brave campaign said on its official Facebook page that there has been no official information regarding his arrest, prosecution or his being at any of the country's morgues.

Following the ouster of president Hosni Mubarak in February 2011, Massouny, a university student at the time, was politically active and participated in several youth-led protests.

He was briefly detained in July 2011 while filming a protest against the Supreme Council of the Armed Forces in Luxor. He was also arrested briefly in August 2011 after the dispersal of a Tahrir Square sit-in.

In 2012, Massouny switched his attention to a career as a film editor.

In June 2015, the Freedom of the Brave campaign issued a statement on recent cases of political activists disappearing, stating that 163 cases have been documented since April. In some of the cases, the activists have resurfaced, while the rest remain missing.

The centre-left Constitution Party issued a statement on Tuesday condemning the disappearance of Massouny and demanding his immediate release.

"For more than three months, nobody has known the whereabouts of Mostafa Massouny," read the statement, adding that forced disappearances are a crime against the constitution and the law.

Several prominent Egyptian TV hosts like Khairy Ramadan and Gaber El-Armouty also commented on the case, demanding answers for Massouny's disappearance.