Peering out from one of the perimeter walls of Sana'a University is a young man's face, stencilled in black and white paint. Daubed next to him is his name and the year he disappeared. A metre on is another face, and then another, and then another, stretching along the whole perimeter of the wall.

The faces belong to Yemeni political prisoners who simply vanished, leaving behind families who have little or no knowledge of their fate. Some go as far back as the 1970s and some date to the Yemeni revolution against former president Ali Abdullah Saleh in 2011.

They are part of a campaign called The Walls Remember Their Faces, the brainchild of a 26-year-old street artist, Murad Sobay.

"The meaning of the word 'wall' has changed. A wall was a prison, a barrier – now a wall is a way of expressing yourself, a wall is inspiring. The walls hold the memory of the disappeared political detainees better than people can," he explained.

The campaign has spread across the streets of Sana'a and other cities in Yemen. It is not Murad's only campaign; Colour the Walls of Your Street was an attempt to use street art to beautify areas that had been affected by armed clashes in Sana'a in 2011. His most recent campaign, 12 Hours, aims to highlight Yemen's "ills", each hour focusing on a different issue such as sectarianism, the kidnapping of foreigners and US drone strikes in the country.

Part of Murad Sobay's 12 Hours campaign, highlighting sectarianism. Photograph: Abubakr al-Shamahi for the Guardian

"After the revolution, I found that the soul of the Yemeni people was broken because of war, the circumstances, the situation inside the country," said Sobay. "I found that the buildings and the streets were full of bullets, full of damage. So I went on Facebook and said I would go on to the streets to paint the next day and I did."

While there may be doubters that street art can have an effect in a traditional society like Yemen, Sobay is adamant that it is more effective than other methods. "Street art has an amazing ability to highlight an issue in a single moment. Things like sectarianism, I don't need an hour-long lecture, with street art I only need a split second."

Sobay is quick to downplay comparisons to Banksy, he says he is more of a Van Gogh man, but he shares the British artist's passion for using street art to challenge the political status quo. "The revolution has been stolen by ugly people," Sobay said. "They are the same regime but it divided amongst itself."

In turn, the authorities have not been too enchanted by his work, often covering up the artwork.

"It's a sensitive issue for them," he said. "It makes them fearful. The eyes of those who disappeared watch the killers, the officials with blood-soaked hands, right in front of their houses."