113 of the 276 Chibok schoolgirls kidnapped by terror group Boko Haram remain unaccounted for.
82 were freed in May and 21 others were released last year.
The girls were kidnapped from a school in Chibok in April 2014 and 60 of them managed to escape.
The Bring Back Our Girls (BBOG) group on Thursday observed a sit out to mark the 1 200 days since the abduction of the girls.
Meanwhile, security researcher Liesl Louw-Vaudran says some government authorities have argued that too much publicity "raises the stakes" in hostage situations.
She explains that without publicity, hostage victims can become forgotten.
Louw-Vaudran says the Bring Back our Girls campaign put Boko Haram in the spotlight.
Take a listen to her explore the implications of terrorist abductions and rescue efforts:
At the same time, counselling psychologist Jeremy Bayer says some hostages can develop Stockholm syndrome.
It is described as feelings of trust or affection by a victim towards a captor in many cases of kidnapping or hostage-taking.
Take listen o him explain: