No group has claimed the four activists' abduction and they have not been heard from since.
Ankara-backed rebels played a key role in supporting Sharaa's Islamist group Hayat Tahrir al-Sham (HTS), which headed a rebel alliance that seized Damascus on December 8, toppling longtime ruler Bashar al-Assad.
The seismic change in Syria is expected to yield deeper Turkish sway just as a change of US administration is raising questions over how long Washington will keep backing the country's Kurdish-led forces.
Assad fled Syria following a lightning offensive spearheaded by the Islamist Hayat Tahrir al-Sham (HTS), more than 13 years after his crackdown on democracy protests precipitated one of the deadliest wars of the century.
Darwish was detained for months by one of the most feared branches of the former government's many-tentacled intelligence services.
Syrians will not miss Assad, a brutal ruler who failed his people.
The offensive, which took just 10 days to sweep across Syria and take the capital Damascus, stunned the world and brought an end to more than a half a century of brutal rule by the Assad clan.
"We would like to see the situation in the country stabilised somehow as soon as possible," Kremlin spokesman Dmitry Peskov told reporters.
"Their human capital, their experience will allow the country to flourish," Bashir said in an interview published Wednesday.
The Islamic State group on Thursday released an audio message purportedly from its leader, Abu Bakr al-Baghdadi, who has not been seen or heard from in months.
Fresh efforts to revive peace talks on Syria is due to begin in Geneva.
Islamist rebels in Syria takes over much of the key north-western town of Jisr al-Shughur, activists say.
Islamic State (IS) has lost more than a quarter of its territory in Iraq since US-led coalition air strikes began in August, the Pentagon has said.
According to Israeli military assessment, Israel could suffer hundreds of civilian dead if it fights another war with Hezbollah.
A monitoring group says, since last three months, the Islamic State has recruited at least 400 children in Syria and trained them as so-called "Cubs of the Caliphate" and hard line indoctrination.
Nine British medical students and doctors are feared to has travel to Syria to work in areas controlled by Islamic State militants.
The US defence department says it is investigating an online threat allegedly made by Islamic State to about 100 of its military personnel, and posted a list of the names and addresses on a website linked to the group alongside a call for them to be killed
Chechen woman living in Netherlands takes her two young children against their father's will to join Islamic State (IS) militants in Syria
Three teenagers who were stopped from travelling to Syria from Turkey are flown back to the UK and arrested, Scotland Yard says
