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.
US President Barack Obama says the Russian bombing campaign in Syria in support of President Bashar al-Assad is driving moderate opposition underground and "only strengthening" Islamic State.
Donald Trump says he would send home all Syrian refugees the US accepts, if he becomes president.
Russia appears to have begun carrying out air strikes in Syria against opponents of President Bashar al-Assad, a US defence official says.
President Vladimir Putin secures parliament's unanimous backing to launch air strikes against Islamic State militants in Syria, paving the way for imminent Russian military intervention in its closest Middle East ally.
US President Barack Obama has said defeating Islamic State in Syria would only be possible if President Bashar al-Assad stepped down.
Russia is considering whether to follow the US and its allies in conducting air strikes against Islamic State (IS) targets, President Vladimir Putin says.
France claims to have carried out its first air strikes against the Islamic State group in Syria following nearly three weeks of surveillance flights.
European Union leaders pledge another €1bn (£700m, $1.1bn) to help UN agencies support Syrian refugees in the Middle East, as part of renewed efforts to tackle the EU's migrant crisis.
Splits within the EU on the relocation of 120,000 migrants are further exposed as leaders gather for an emergency meeting in Brussels.
European Union ministers are to meet to try to resolve a dispute over how to relocate 120,000 asylum seekers who have recently arrived in Europe.
