['When I was about seven years old, my cat Hector got out of the house and got lost in the neighborhood.', 'Oh no! Were you able to find him ever?', "Unfortunately we weren't. We put out signs but never were able to track him down."]
Aw I'm sorry to hear that. Losing a pet is never an easy thing, especially when you don't know what happened to him.
When I was seven years old, my cat ran away.  We put up posters around the neighborhood but never found him.  It was really tough for me since I had known him since I was born.