Manon, an eight-month-old whippet, vanished from Hampstead Heath at the end of June while out with a dog walker. His collar was found later, leading to fears he has been stolen.
When he heard of the news, Extras star Ricky immediately stepped in to help and used Jonathan's Radio 2 show to do so.
Announcing he was making an appeal, he told Jonathan about Manon, adding: "It's fawn and it's got little tiger stripes and grey eyes. It's beautiful."
On discovering that Ricky had put up £1,000 towards the reward money, Jonathan straight away matched the amount. He also urged listeners to keep an eye out in case they saw the puppy.
Owner Terri Begg was delighted with the stars' generosity. "It's wonderful and lovely and I am very grateful to them," she said."