In an open letter to the girls, she criticised Nigeria's authorities and the international community for not doing enough to secure their release.
The Boko Haram militants caused global outrage after abducting the girls from Nigeria's north-eastern Chibok town.
The UN estimates that the insurgency has now displaced 800,000 children.
"We cannot imagine the full extent of the horrors you have endured. But please know this: we will never forget you," Ms Yousafzai said in the letter to the 219 girls who were abducted during a night-time raid on their boarding school.
She added that there were reasons for "hope and optimism", after recent successes by Nigeria's military in regaining territory from Boko Haram.
"I look forward to the day I can hug each one of you, pray with you, and celebrate your freedom with your families," Ms Yousafzai said.
In Nigeria, campaign group Bring Back Our Girls has launched a week of events encouraging people to remember the girls ahead of the first anniversary of their abduction on Tuesday.
A vigil and candlelit procession is due to be held in the capital Abuja.
The UN children's agency, Unicef, said the abduction of the schoolgirls from Chibok was "only one of the endless tragedies being replicated on an epic scale across Nigeria and the region".
The number of children fleeing the Boko Haram insurgency has doubled in the past year and more than 1.5 million people have now been displaced in the six-year conflict, Unicef said in a report.

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Governing body the UCI introduced the ban in 2011, but a whistleblower said Team Sky continued to inject riders.
One of the substances said to have been injected is Fluimucil, at the heart of the controversy over a mystery package delivered to Bradley Wiggins in 2011.
Team Sky had been renowned for their robust no-needle stance.
In March, British cyclist Josh Edmondson told the BBC he broke the sport's rules by secretly injecting himself with a cocktail of vitamins when riding for Team Sky.
The substances are not illegal under World Anti-Doping Agency (Wada) rules but there are concerns about the ethics of administering them intravenously.
Ukad and the UCU are investigating claims by Edmondson that Team Sky covered up his use of banned injections.
Team Sky deny doing so, insisting that Edmondson did not confess at the time, and that they did not report the case because of concerns about his mental wellbeing.
PA's source, who sent the information to the House of Commons' Culture, Media and Sport Select Committee and Ukad, is understood to have worked for Team Sky.
The source said some Team Sky doctors were using intravenous recovery methods towards the end of the team's difficult first season in 2010 and continued to do so despite the UCI ban, which Team Sky publicly supported.
The source has claimed Team Sky hired Dr Fabio Bartalucci in late 2010 as he was believed to have expertise in IV recovery.
The Italian, who was picked up by police in an anti-doping raid at the 2001 Giro d'Italia but not charged, left in 2011.
Ukad said it "does not discuss or disclose information in relation to its investigations".
Culture, Media and Sport Select Committee chairman Damian Collins said: "This raises further concerns about how Team Sky policed the use of medication for riders outside of competition, and how hard they were prepared to press up against the line of what was allowed or acceptable."
BBC Sport attempted to contact Team Sky. However, a spokesperson earlier told PA: "It is right that any concerns are reported to and dealt with by the appropriate authorities, and we will continue to co-operate with them."

The 71-year-old was crushed under the vehicle as she crossed Princes Street opposite the Waverley Steps and beside the Balmoral Hotel on Thursday.
The crash happened at about 12:15 and the road was closed for two hours.
Sgt Iain Blain, of Police Scotland, said: "This collision has left a woman with serious injuries and we are keen to hear from anyone who witnessed it."
Nobel Peace Prize winner Malala Yousafzai has called for more action to free schoolgirls abducted by militant Islamists in Nigeria a year ago.
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The UK Anti-Doping Agency (Ukad) is investigating claims Team Sky may have breached cycling's 'no needles' policy, according to the Press Association.
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A woman who was knocked down by a taxi in Edinburgh city centre is in hospital with multiple serious injuries.