‘Where is Navalny?’ A Search Is On for the Missing Russian Dissident.

After two weeks without word from Aleksei A. Navalny, Russia’s most prominent opposition figure, his lawyers and allies, fearing the worst, are running a frantic campaign to find him.

Their efforts have included requesting information from dozens of Russian prisons and taking to social media to raise awareness of Mr. Navalny’s disappearance and to call on the Russian government to reveal his whereabouts.

Many Russians living abroad have gone to their country’s diplomatic missions to protest. Some have held up posters saying “Where is Navalny?”

Dmitri S. Peskov, spokesman for President Vladimir V. Putin, told journalists on Friday that the Kremlin had “neither the possibility, nor rights or desire to trace the fate of convicts,” referring to Mr. Navalny.

Here is what we know about Mr. Navalny and his disappearance.

When did Mr. Navalny disappear?

The last time Mr. Navalny’s lawyers heard from him was on Dec. 5. The following day, one of his lawyers waited for seven hours outside the penal colony where Mr. Navalny was being kept but was not allowed to see him, Kira Yarmysh, a spokeswoman for Mr. Navalny said. Mr. Navalny then failed to appear by video link at a scheduled court hearing the next day, Dec. 7.

In the days after Mr. Navalny’s disappearance, his allies grew more alarmed as letters sent to him went undelivered and the authorities declined to reveal his location to his lawyers. On Dec. 11, officials in the prison colony that had been holding Mr. Navalny — in Melekhovo, a town about 160 miles east of Moscow — told his lawyers that he was no longer listed among its inmates, Ms. Yarmysh said.

Mr. Navalny was scheduled to appear for various court hearings on Monday, she added. One of the courts at which he was supposed to appear suspended his case because it could not locate him, Vyacheslav Gimadi, a member of Mr. Navalny’s legal team, posted on social media.

Where could he be?

As part of his last sentence, delivered by a Russian court in August after a conviction for supporting “extremism,” Mr. Navalny was scheduled to be transferred to one of Russia’s “special regime” colonies, known for their harsh treatment of inmates. There are at least 25 such prisons, scattered across Russia from the country’s European part to the Arctic Circle and the Far East.

But he had not been moved by early December. Mr. Navalny suggested in a series of social media posts in November that the reason was because Russian investigators were unwilling to travel to remote special regime colonies as they pursued further cases against him.

If he has now been moved to one of those penal colonies, that might explain his current disappearance.

Detainees being transferred to remote prisons in Russia can spend long weeks being shuttled between trains in special prison rail cars and have little or no access to the outside world.

By law, relatives should receive notification within 10 days after an inmate’s arrival at a new destination, usually by mail, and such a letter can take up to 20 days to arrive, said Yevgeny Smirnov, a Russian lawyer. According to Mr. Smirnov, the Russian prison system considers information about such transfers a state secret.

“A transfer between prisons is the most dangerous time for a convict,” Mr. Smirnov said in a response to written questions. “During that period, they change a multitude of transit points and remain without any way to contact the outside world,” he added. He also noted that, based on past experience, prisoners could be in transit and incommunicado for two to three months.

Last week, Baza, a Russian news outlet, reported that Mr. Navalny had been transferred to a detention center in Moscow to await trial on another criminal charge. But Ivan Zhdanov, the head of Mr. Navalny’s anticorruption foundation, reported that the group had checked all Moscow detention centers without finding him.

On Saturday, Olga Romanova, a Russian prison rights activist, said on Facebook that Mr. Navalny was undergoing treatment in a prison hospital in the city of Vladimir, near Melekhovo. But that assertion has not been verified.

Why was Mr. Navalny imprisoned?

Mr. Navalny, 47, is the only Russian opposition figure of the past decade to mount a significant political challenge to Mr. Putin. He established a robust organization, drawing thousands of Russians to his rallies nationwide, and engaged many young people in politics.

He has been in custody in Russia since his detention in January 2021 in a Moscow airport, where he arrived after spending months in Germany recovering from poisoning by a nerve agent. Mr. Navalny and Western governments accused the Kremlin of poisoning him, which Russian officials denied.

Since then, the Russian authorities have brought forth a multitude of new charges against Mr. Navalny. According to Ms. Yarmysh, he is currently a defendant in 14 criminal cases and faces potential sentences of up to 35 years in prison.

What activities did he pursue in prison?

Since entering the Russian prison system, Mr. Navalny has filed a string of lawsuits against the authorities.

A lawyer by profession, he has filed suits demanding access to decent dental care, complaining about loudspeakers in his cell that repeatedly aired Mr. Putin’s speeches and protesting against wiretapping in a room he uses to meet with lawyers.

Despite his imprisonment in increasingly harsh conditions, Mr. Navalny has remained a significant voice in Russian political life. With the help of his lawyers and political allies, he has published articles and manifestoes, and regularly posts on social media.

Since Mr. Navalny’s disappearance, his allies have called on his followers to vote for any candidate other than Mr. Putin in the presidential election in March, aiming to amplify the visible dissent against Mr. Putin’s policies, including the invasion of Ukraine.