Tice, 31, entered Syria in May, where he has filed articles on the conflict between opposition fighters and soldiers loyal to President Bashar Assad for The Washington Post, McClatchy Newspapers and other outlets, the Post reported.
He was to have returned to the United States in mid-August. However, family members and news organizations said Thursday they have not heard from Tice in more than a week.
"We're focused intensively on trying to ascertain his whereabouts and ensure his safe return," Post Executive Editor Marcus Brauchli said in a statement. "Austin is a talented and courageous journalist whose work has helped to shape the world's understanding of this humanitarian and political crisis."
Anders Gyllenhaal, McClatchy vice president for news, said in a statement that the company is "deeply concerned" about Tice's safety and that McClatchy has sought help from the U.S. State Department to find him.
State Department spokeswoman Victoria Nuland said officials "are working through our Czech protecting power in Syria to get more information on [Tice's] welfare and whereabouts, and we greatly appreciate the efforts of the Czech mission on behalf our citizens."
The U.S. Embassy in Damascus suspended operations in February as fighting there intensified. U.S. interests in Syria are represented by the Czech Embassy.
The Committee to Protect Journalists said Thursday the group is concerned for Tice's safety.
"His work is protected by international law, which guarantees the right to seek and receive information," said committee Executive Director Joel Simon. "As a journalist, he is a civilian and must be protected from harm."
The group said that since violence broke out in Syria more than 17 months ago, 10 professional journalists and at least 10 Syrian civilian journalists have been killed.
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