Two dogs were allegedly stolen from a property in Selsey on Sunday afternoon.
Darcey Foreman said she contacted police after she returned to her Coxswain Way home to find her previously locked back gate open and her two dogs missing.
However, after wide appeals on social media, one of the dogs, a Labrador named Max, was found safe in the Selsey area and returned home the next day (Monday).
The second dog, a Shih Tzu cross, named Ziggy, is still yet to be found.
Darcey said: "I got home yesterday afternoon to find my back gate was unlocked and the patio doors were open.
"I always leave my conservatory doors open for the dogs to come and go as they please whilst we are out.
"We've been told it was a burglary."
Sussex Police confirmed it received a report of two dogs going missing from a back garden in Selsey and the owner believed they had been 'stolen as a gate to the garden had been opened'.
Darcey's cousin, Dee Cook, told the Observer that the theft particularly affected Darcey's son, who she said was 'devoted' to his dogs.
She added: "It was clearly someone who had been watching her (Darcey)."
Dee said they now believed the Labrador, which was found late last night and returned by a dog warden, was let go because it was 'hard to handle' and not as 'laid back' as the Shih Tzu.
Both Darcey and Dee have asked for anyone who heard or saw anything to come forward.
With there being 'no reports' of these dogs running free in the streets, they believe someone 'must have entered and removed them'.
Both dogs have now been found.