An Isle of Wight businessman has offered a £10,000 reward to help find a teenager who went missing after a night out in Cowes in November 1996.
The donor, who is remaining anonymous, said he had been "incredibly touched" by a Facebook post by Sarah Nettles on her brother Damien's 33rd birthday.
Ms Nettles said the man was "very generous" and "wants to help" the family find Damien's body.
Hampshire Constabulary offered a £20,000 reward, which expired in April.
Police believe Damien may have been murdered, but no one has been charged and the Nettles family do not know where Damien's body is nearly 17 years on.
Ms Nettles said she was "not surprised" the police reward led to nothing as it was public money, which can only be payable on conviction and could not be paid out to the perpetrator of a crime or their family.
Ms Nettles called this new reward "very significant".
She said: "This £10,000 reward will allow anyone to come forward who knows where Damien's body is and give us the ability to find his remains. They can be completely anonymous."
She added: "This is just a really great opportunity for us to have closure, if there is any way in this world that we can know where Damien's body is, that would the next best thing."
A Hampshire Constabulary spokesman said: "We always appreciate every single sincere thought and effort to help the police in any investigation.
"However, we must remain mindful that the 30 pieces of information received in response to a £20,000 police reward only repeated previous unfounded speculation, contained factually inaccurate details, or fell short of police standards for a reliable source."
The anonymous donor said he would provide more information in September about how about how people could deliver information and collect the reward without being identified.
In 2011, detectives arrested eight people on suspicion of murdering Damien, who lived in Woodvale Road in Gurnard, Cowes.
They were questioned over the course of a year and released with no further action.