Dog owner Alun Thomas is begging for witnesses to come forward after the tragic death of his Boxer – Staffy cross, Nicky, on Tuesday.
The dog was inside Mr Thomas transit van as he and other workmen loaded a trailer with earth after doing work on someones garden.
During a three minute window throughout the work, two men stole the van from Bryn Eglyr in Morriston and drove it towards the motorway.
Upon realising that the dog was inside, they threw her out onto the M4 motorway, Swansea Road, where she was subsequently hit by a lorry and killed.
Mr Thomas, who has cared for the seven year old dog for five years, said that she followed him everywhere.
“It’s terrible – the dog lived with me and went everywhere with me.”
“The people who threw the dog onto the motorway were wrong. I just want them caught.”
The owner has urged anyone who witnessed the incident to call South Wales Police on 101 or Crimestoppers on 0800 111 555.