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 man identified as extremist "Jihadi John" said he felt like a "dead man walking" after being contacted by UK security services
CCTV pictures have emerged showing three UK schoolgirls on the Turkish leg of what is believed to have been their journey to join Islamic State in Syria
The masked Islamic State militant known as "Jihadi John", who has been pictured in the videos of the beheadings of Western hostages, has been named.
Fears are growing for the safety of three east London schoolgirls who police believes are trying to cross the Turkish-Syrian border to join Islamic State (IS).
President Barack Obama says US 'not at war with Islam - we are at war with people who have perverted Islam
