Scott Rainford candidly revealed he had been on the verge of taking his own life on the day his father bought him Zedd, a Beagle and Cocker spaniel cross.
Scott and Zedd, now 10 months old, moved to a flat on Mark Close, Penwortham, around a month ago.
But on Thursday night Zedd, who was chained to an extendable lead to allow him to roam a short distance outside the flat, went missing and there has been no trace of him since.
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It remains unclear whether it was an opportunist thief or a targeted incident.
Scott, 30, who also has autism, said in the run up to the puppy's disappearance from his home on Mark Close, Penwortham, a note had been left in the letterbox saying the dog had 'not stopped barking'.
He said: "Zedd is only 10 months old and he means the world to me, he saved me.
"I have suffered severe depression since the age of eight and until I got Zedd I had no memories of ever feeling joy and happiness.
"The day before I got Zedd I had written my own will and a note to my family, but suddenly my dad took me to a dog breeder, unexpectedly.
"I walked into the pen and Zedd chose me, he was the first dog that came up to me and I said: 'I'm not leaving without him.'
"My life began to change when I got Zedd, I got a lot of confidence, started participating in things, and wanted to try to pursue a career in the local council."
Zedd was clipped to his outside cable and harness and it is suspected someone unclipped him in the moments Scott went to the bathroom.
He added: " I put my shoes on and ran to the main road because at first I thought he may have gotten off his leash. My heart was racing when he wasn't there.
"I'm worried sick."
The desperate family has put up posters, and searched high and low for the animal, and shared posts on social media campaign to find Zedd.
The matter was also reported to Lancashire Police.
Anyone with information can call 101.