Seven Syrian activists collaborating with the Avaaz action group were found "executed" in Homs, while two others, including a foreigner, remain missing, the non-governmental organisation said on Thursday.
The group of nine men, including one foreign paramedic, had set off on foot for Baba Amr on Wednesday morning after hearing that two foreign journalists were killed in the flashpoint district of Homs, said Avaaz's Alex Renton.
"They carried a respirator and medicines," he said.
After losing contact with them, a member of the network on Wednesday "found seven of them shot dead, with hands tied behind their backs... just before the entrance to Baba Amr," the activist told AFP.
He said the respirator was gone while some medicines were found "strewn across the road."
He declined to reveal the name or the nationality of the foreign paramedic, but said his embassy had been alerted.
"Those were civilian activists, unpaid volunteers," he said, accusing the "Shabiha (pro-regime militia) or armed forces" of killing the men whose ages ranged between 16 and 24.
Renton said Avaaz been working on training and equipping volunteers on first aid and citizen journalism, adding the group has had a network of 200 amateur reporters, but that many have been arrested or killed.
The group also transports medical aid from across the border with Lebanon to areas afflicted by violence.