The 33 year old and newest Tearfund ambassador embarked on the journey on Wednesday morning as he bid farewell to his Ulster team. He will be moving to France to play for Montpellier next season.
Tearfund has dubbed the ride 'Cycle for Freedom' which will cover the length of Northern Ireland's North Coast.
Pienaar said as a father of two it's important to do his part to help protect vulnerable children.
He said: "Trafficking is a global crime that affects the world's most vulnerable. I am so moved by the many who have signed up for the Cycle for Freedom and believe that, together, we can make a real difference."
A group of 30 cyclists from across Northern Ireland, including the player's teammates Rob Herring and Craig Gilroy, helped him raise £20,000 for the cause. Tearfund said the money raised could help protect up to 2,500 children at risk across the world.
The organisation said: "The epic bike ride will help protect children like Mazna, a young girl Tearfund rescued after she was trafficked from her small village in rural India.
"Mazna's father sent her to a large city to pursue a job as a home help, in the hope she would find better opportunities than he could offer and a release from economic poverty. But Mazna was immediately sold to a brothel."
