By Co-Founder and CEO of the Global Poverty Project Hugh Evans and UN Population Fund Executive Director Dr. Babatunde Osotimehin

Kadiga, 17, was subjected to Female Genital Mutilation as a child. Like millions of girls in a similar situation, she will face countless risks to her health and untold pain as a result of decisions taken about her by others. But opinions in her community in Afar, Ethiopia, have recently started to change and, as a result, her younger sister, Medina, will not be cut. Her future will be happier, safer and freer than that of her older sister, as her community has seen that her well-being matters.

If we invest in young people, they can do phenomenal things. Just look at the Rwandan teenagers campaigning for the rights of girls in their communities, or the 15-year-old girl in Niger who rejected child marriage and now is a mentor of other adolescent girls, or the scientific inventions of a 12-year-old.

Today's young people are a powerful force, both individually and collectively. But if we were to take a snapshot of the 1.8 billion people aged 10 - 24 today, you would see an incredibly unequal picture. From Cambodia to Cameroon, Malaysia to Madagascar, millions of today's youth are still lacking access to basic rights, and don't have a genuine chance to reach their potential in life.

The issues faced by young people today are varied and far reaching. In countries like Uganda, Ethiopia and others, girls like Kadiga and Medina are more likely to die in childbirth than they are to finish school, and an estimated one in three girls are married before the age of 18, some as young as eight. These unacceptable statistics tell us that we're failing the youth of today. They're not getting the development opportunities they deserve.

In 2015, we have a major opportunity to change this and ensure that every young person can dream and achieve. The creation of the United Nations post-2015 development agenda will address some of the most critical issues of our time - climate change, health, education, gender equality, human rights - and young people stand to gain or lose the most. The decisions made will shape the formative years for today's young people, so we must not allow their views to be ignored.

Medina was spared the dangers and indignities faced by her sister as a result of the growing international understanding that her rights - and her potential - matter. This change in mindset has begun, but it must continue and increase.

Today, in recognition of International Youth Day, Global Citizen is proudly joining forces with UNFPA, the United Nations Population Fund, to create an overwhelming demonstration of support for governments to invest in the rights and needs of young people.

#ShowYourSelfie is a visual petition with a difference. It's a platform to bring young people together, amplify and empower them to be seen and have their voices heard.

Technology is bridging borders and changing the way that we connect with the world. No longer are young people in distant countries so distant. We can share stories, faces and voices increasingly easily across borders. The recent emergence of "selfies" - an instant way to share with the world where you are, what you're doing and who you're with - has the power to be the perfect mechanism to tell a global story of young people everywhere.

Our concept is simple. Your selfie is your personal signature to show you believe in the power of Kadiga and the rest of the world's 1.8 billion young people. Thousands and thousands of photographs, from all corners of the globe, will send a clear message to leaders that it's time to put young people in the spotlight.

This message will be delivered to world leaders and decision-makers over the next year, and the "visual petition" will be delivered to them in September 2015 during the General Assembly, calling on all governments to invest in specific policies addressing the rights and needs of young people. Specifically, our visual petition will ask for youth needs to be included across every new development goal. This means calling for inclusion in the Post-2015 Development Agenda of education, employment skills and opportunities, quality healthcare, including access to contraception, comprehensive sexuality education, protection from violence and harmful practices and participation in decision-making.

Over the next few months, we'll be mobilizing young people everywhere, allowing them to show world leaders that their needs and rights have to be a priority. We cannot allow history's biggest generation of young people to be invisible - #showyourselfie at www.showyourselfie.org

This joint op-ed was originally published on the Huffington Post .