Leah Sharibu was among 110 youngsters kidnapped by Boko Haram in the north-eastern village of Dapchi on 19th February this year.
Last month, the children were freed - all of them except five who died in the incident and Leah, who refused to denounce her beliefs in exchange for her freedom.
Dame Caroline Spelman MP, a Christian and the Conservative MP for Meriden, wrote in a blog: "On her 15th birthday, we must stand in solidarity with Leah Sharibu, the courageous young girl who is surrounded by terrorists renowned for their extreme brutality, yet refuses even to pretend to convert in order to regain her freedom.
"We must call ever more strongly for her release and safe return. And we must not stop until she is home."
Happy Birthday Leah, the Lord is your shield and guide. #FreeLeah#Dapchigirls. pic.twitter.com/j1nWt0SCjE
— JOE D CHONG (@JOEDCHONG) May 14, 2018
Mervyn Thomas, chief executive of Christian Solidarity Worldwide (CSW) - an organisation which has been highlighting Leah's plight - wrote on Twitter: "It's Leah Sharibu's 15th birthday today, but she won't be celebrating with her family.
"For three months, she's been held prisoner by Boko Haram. She hasn't been released as she refuses to convert in exchange for her freedom."
Leah Sharibu has been held by Boko Haram since February because she refuses to renounce her #Christian faith. Monday is her 15th Birthday #Nigeria Must secure her release. Please RT pic.twitter.com/C1CsBBcb3z
— Susan Hall AM (@Councillorsuzie) May 12, 2018
Supporters have marked the teenager's 15th birthday by sharing pictures of her on social media and using the #freeLeah hashtag.
A vicar who is in daily contact with Leah's father Nathan told CSW: "I met with him recently he confirmed the fact that his daughter had refused to deny Christ and that that is why she has not been released."
It's Leah Sharibu's 15th birthday today, but she won't be celebrating with her family. For 3 months she's been held prisoner by Boko Haram. She hasn't been released as she refuses to convert in exchange for her freedom. #FreeLeah #DapchiGirls @csw_uk @cswng10 @ECWAHeadquarter pic.twitter.com/fobOVrV8S1
— Claire Denman (@_ClaireDenman) May 14, 2018
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