The singer and former X Factor judge said the world was a better place for having her beloved relative John Boy.
"I ask that whoever did this, has the dignity and strength to come forward. Our God is a loving and forgiving God, but I pray for justice for John Boy and closure for my family."
Scherzinger has begged for information relating to the fatal incident, which she said took place in Fort Lauderdale in Florida.
She has also paid tribute to her cousin, who she said was an "incredible man".
Posting on Instagram, the singer said: "It's like a nightmare, that we will never be able to wake from.
"It is with the heaviest of hearts that I say goodbye to my beautiful cousin, John Boy.
"Though I must take comfort in knowing that he is at peace with our Lord, I also know the agony our family is going through, knowing someone hit him head on and just left him there to die.
"My sweet cousin, I love you so much. This world was a better place with you and your kind, creative heart in it. We will never forget you and will carry you with us forever."
Scherzinger has posted a picture of her late cousin, with a further message carrying information on the alleged incident in Florida, including information from Broward Crime Stoppers about the car allegedly involved.
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