Before his detention, Mr. Tashi had written on his microblog that Tibetans needed to protect their culture and that Chinese officials should aid them in doing so. He has argued for greater Tibetan autonomy within China, but none of his known writings have called for Tibetan independence, which he has said he opposes.

The family said it had not been able to find a local lawyer to represent Mr. Tashi. Officials have not yet announced a trial date.

Mr. Tashi’s case has attracted international attention. Officials at the State Department are aware of his detention, and a representative of Canadian Journalists for Free Expression said the group was starting a petition to call for his release. President Obama may raise human rights issues with his Chinese counterpart, President Xi Jinping, when Mr. Xi visits Washington this week for a summit meeting on nuclear issues.

As an advocate for Tibetan culture, Mr. Tashi has been most vocal about language education, saying that schools should adopt a true system of bilingual education so that Tibetan children can become fluent in their mother language.