The parents of Austin Tice, a 31-year-old American freelance journalist who has been missing in Syria for three months, said Monday that the Syrian government told them that it had no information about his whereabouts. The parents, Marc and Debra Tice, who traveled from Houston to Beirut, Lebanon, said at a news conference that they would travel to Syria if necessary to be reunited with their son. The missing journalist, a former Marine whose articles on the Syria conflict and the insurgent Free Syrian Army have been published by several news organizations, was last heard from on Aug. 13. A video that showed a person said to be Mr. Tice, apparently in the custody of Islamist militants in Syria, surfaced on Oct. 1, but its authenticity was never confirmed. American officials initially said they believed that Syria’s government had detained Mr. Tice, who entered Syria without official permission. Last week, a State Department spokeswoman, Victoria Nuland, said she had been urging the Syrian government “to be more forthcoming” with any information it might have about Mr. Tice.