A dog lover is searching for a speeding motorist who hit and killed her puppy before driving off, leaving her four-year-old son heartbroken.

Dobby had escaped from the family home in Bush Road, Cuxton on Sunday when he was knocked down by a passing car at about 8.30am.

The male driver of the dark grey BMW stopped briefly but then drove away without getting out of his car. Nine-month-old Dobby, a whippet named after the house elf in Harry Potter, was killed instantly.

Dobby’s owner Karen Copeland has posted a desperate appeal on Facebook to try to track down the man behind the wheel. Her post has been shared more than 1,000 times but she is yet to trace him.

Mrs Copeland, mum to Harry, aged four and Sophie, two, posted online: “Today I had to explain to a four-year-old how someone hurt his pal and how he is now in heaven. To the person responsible, what goes around comes around and one day I hope you get what you deserve.”

She added: “If anyone knows anything please let us know. A car speeding down Bush Road in Cuxton ran over and instantly killed our dog, Dobby. Someone in Cuxton must know who it was. Please share so we can find out who it was.”

The family has been left devastated by Dobby’s death. On the day he was killed, they were having a party for Sophie’s birthday.

Mrs Copeland, 32, said: “Sophie didn’t really understand, she just thought the dog had been hurt. But I had to tell Harry before the party. We told him Dobby was in heaven and was being looked after by his grandad. They were close, Harry loved taking Dobby for walks in the woods.”

“I’m just hoping someone sees the post and knows who it was. It has already been shared 1,400 times, which shows the power of Facebook.”

The man has been described by a witness as in his 30s with dark hair and a beard.

A police spokesman said: “Initial inquiries have been carried out but the car has not been identified. If any further information comes to light then it will be reviewed accordingly.”