Stanley the 18-month-old chihuahua disappeared from a park in Woodridge on 12 April, as reported in the East Anglian Daily Times.
His owner Christie Barr and her family set up a Facebook page to appeal for help to track him down.
He was found walking alone on 12 July and handed to a vet in St Albans who identified him through his microchip.
Microchipping of dogs has been compulsory in the UK since April 2016 to help trace the owners of lost pets.
Ms Barr said Stanley was being looked after by her mum while she was on holiday, who saw him being taken away by a young boy on a bike.
"We're just so glad to have him back and he's healthy and alive," she added.
"I think maybe he was taken, sold on, used for breeding - we're not sure - but he's back and safe and well.
"He's in a bit of shock but he's coming around slowly."
Christie's sister, Roman Woolnough, posted appeals on social media and organised a search to look for Stanley.
She said: "After 13 weeks of blood sweat and tears, we have finally found our baby."
A dog which went missing in Suffolk has been found 100 miles away in Hertfordshire three months later.