Moscow - Concern for jailed Pussy Riot member Nadezhda Tolokonnikova mounted on her 24th birthday on Thursday, after her husband said she could not be found in the prison colony where authorities reportedly sent her in October.
Tolokonnikova has not been seen since being moved on October 22 after protesting alleged prison abuses at her former colony in central Russia and holding a hunger strike.
Tolokonnikova is one of two Pussy Riot members now serving two-year prison terms for performing a protest "punk prayer" in Moscow's Christ the Saviour Cathedral in the run-up to presidential elections last year.
She and fellow bandmember Maria Alyokhina are due for release in March.
Russia's human rights ombudsman said this week that Tolokonnikova was being transferred and was safe. Her husband Pyotr Verzilov believed that she was on her way to a new colony in Siberia.
However having made the trek to the snow-covered Krasnoyarsk region, Verzilov said on Thursday that his wife was not there.
"The authorities of the colony in the taiga [region] told us that they don't have Tolokonnikova and don't know when she will arrive. 19 days without contact with Nadya," he wrote on Twitter.
"Snow, snow, snow, minus 20 degrees and camps where somewhere they are hiding Nadya," he wrote, posting pictures near the colony where Tolokonnikova was said to be headed.
The search in Siberia went on as Tolokonnikova's lawyers submitted legal documents contesting her verdict and sentence made by the Khamovnichesky court in Moscow.
"We are demanding the verdict be annulled," lawyer Irina Khrunova told AFP. She added that her client's transfer could "last a long time" since Russian law does not set any limits on how long its could take.
The conviction and sentencing of Tolokonnikova and Alyokhina on charges of hooliganism sparked an international outcry.
After being jailed, Tolokonnikova penned a letter published in Russian media listing alleged abuses in her old prison colony, including round-the-clock "slave labour" work, beatings, and lack of sanitary facilities.
She went on a hunger strike in protest, ending it only after having health problems and being placed on a drip in the prison hospital.
After that she was transferred, with officials giving no details of her destination.
Her husband, though, said he received information from a reliable source that she was moved to penal colony number 50 in the town of Nizhny Ingash, in Siberia.
Calling for action in Tolokonnikova's case, Amnesty International said this week that "there are serious concerns regarding her safety and wellbeing".
"There are no legal limitations as to how long a prisoner can be in transit," the rights organisation said, calling Tolokonnikova a prisoner of conscience. "The lengthy transit could be a means of pressure and de facto punishment for her recent open letter."
Prison authorities are not required to tell relatives of the convicts' whereabouts until 10 days after transferring them to a new place.
A group of Tolokonnikova's supporters staged fireworks for her birthday near the headquarters of the prison service in Moscow in the early hours of Thursday.