A woman describing herself as a cousin said Amina Abdallah was seized Monday by men who appeared to be security agents, CNN reported.
"Amina was seized by three men in their early 20s," Rania Ismail said. "One of the men then put his hand over Amina's mouth and they hustled her into a red Dacia Logan."
Abdallah, an English teacher, holds dual citizenship in Syria and the United States.
In blog posts and in an interview with CNN last month, Abdallah described earlier attempts to abduct her. She said she and her father had gone into hiding.
"We are hoping she is simply in jail and nothing worse has happened to her," Ismail wrote. "Unfortunately, there are at least 18 different police formations in Syria as well as multiple different party militias and gangs. We do not know who took her so we do not know who to ask to get her back. It is possible that they are forcibly deporting her."
Since violent protests began in Syria against the government of President Bashar Assad, about 1,200 people have been killed.