The donation has been made by Lord Ashcroft, founder and chairman of Crimestoppers, and will be offered through the charity for information that leads to the conviction of those responsible for the schoolgirl’s death.
Olivia was fatally shot in her home in Dovecot, Liverpool, on Monday August 22.
Her mother, Cheryl Korbel, 46, was injured as the gunman chased convicted burglar Joseph Nee into their property at about 10pm.
Lord Ashcroft said: “Olivia’s murder has shocked us all, which is why I have made this personal offer of up to £50,000 available via Crimestoppers to help get justice for Olivia’s family and friends.
“What happened is truly unacceptable and I say to anyone who has information that can help catch the killer to come forward completely anonymously.”
Crimestoppers, which allows people to give information anonymously, said the appeal is aimed at those in the community who have previously been too scared to come forward.
The charity’s director of operations, Mick Duthie, said: “We know it can be difficult to speak up about someone who is involved in serious crime, especially if they are close to you.
“Crimestoppers has kept our promise to protect your identity since we started back in the late 1980s. Around half a million people contact our charity every year to pass on what they know.
“If you know who was involved in Olivia Pratt-Korbel’s murder, please speak to us completely anonymously.
“Nobody will know you contacted us, and you will be doing the right thing for Olivia, her family, friends and the wider community across Liverpool who are still trying to come to terms with this tragedy.”
Merseyside Police have arrested nine men as part of their investigation into her death but all have since been bailed.
This week, officers have been searching at West Derby Golf Club for the two guns used in the attack.
Olivia’s funeral is due to be held at St Margaret Mary’s Church in Knotty Ash on Thursday.
The reward will be given for information leading to the conviction of Olivia’s killer that is given exclusively to Crimestoppers, by calling 0800 555 111 or online at crimestoppers-uk.org/give-information/forms/give-information-anonymously.