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.
A deputy leader of Islamic State (IS), Fadhil Ahmad al-Hayali, has been killed in a US military strike in northern Iraq, the White House says.
Islamic State (IS) militants in Syria have demolished a Christian monastery in al-Qaryatain town in Homs province.
Eight Turkish soldiers have been killed in a bomb attack in the south-eastern province of Siirt, the army says.
The World Health Organization is calling for "intensified action" to protect health workers treating people in crisis and conflict zone.
A Syrian government warplane crashes in a marketplace in the north-western town of Ariha, killing 17 people.
Turkish air force jets carry out fresh strikes against Islamic State (IS) positions in Syria and also hit Kurdish militants in northern Iraq.
Turkish planes have for the first time carried out air strikes against Islamic State (IS) group targets in Syria.
A nurse who said he was forced to work with the so-called Islamic State is thought to be returning to Australia.
A US air strike reportedly kills Muhsin al-Fadhli, the Kuwaiti leader of the Khorasan Group, a shadowy al-Qaeda offshoot operating in Syria.
Turkish PM Ahmet Davutoglu promises to boost security along the country's border with Syria, after 30 people were killed by a bomb in the town of Suruc.
