Marina Ovsyannikova, an editor at state-controlled Channel 1, was detained after she ran on to the set on Monday holding an anti-war sign.
The sign, clearly visible for a few seconds, read: "No war, stop the war, don't believe the propaganda, they are lying to you here."
Her whereabouts are now unknown.
Ms Ovsyannikova's lawyers say they have been searching for their client but have been unable to find her.
One of them, Anastasia Kostanova, told BBC Russian she had been trying to reach Ms Ovsyannikova by phone but her calls had gone unanswered.
s Kostanova said she "spent the whole night looking" for the missing journalist.
"This means that they are hiding her from her lawyers and trying to deprive her of legal assistance and, apparently, they are trying to prepare the most stringent prosecution," Ms Kostanova said.
Another lawyer, Pavel Chikov, posted on Twitter that he was unable find Ms Ovsyannikova.
"Marina Ovsyannikova has not yet been found. She has been imprisoned for more than 12 hours," he said on Tuesday morning.
Police arrested her over a new law that bans calling Russia's military action in Ukraine an "invasion" or spreading "fake news" about the conflict.
Though the strictest punishments carry a potential prison sentence of up to 15 years, Mr Chikov said Ms Ovsyannikova was likely to be fined 30,000 to 60,000 roubles (£205-£410).