Migrant justice activists are searching for Hugo Castro, a U.S.-based immigrant rights activist with the group Border Angels, who disappeared in Mexico on Thursday. He disappeared after posting a Facebook video asking for help, saying his life was in danger. He’d previously received death threats for his work to support refugees traveling through Mexico en route to the United States. He disappeared while he was traveling to join a caravan of Central American refugees who are heading to the U.S. to apply for asylum.