The Rapponottis believe the thieves may have been a man and woman, since Karen's makeup was also stolen, and that they may have taken Sydney to keep as a pet.
Losing Sydney is especially hard on Mike.
The U.S. Marine Corps veteran served three deployments in Iraq and Afghanistan and suffers from post-traumatic stress disorder-like symptoms.
Sydney would ride with him while he worked at his truck-driving job and help him stay calm in tense situations.
"I get hypersensitive because of what I did in the military," Mike Rapponotti said. "I can't be around large groups of people, frustrating situations. For me, it was mostly someone to relax with at the end of the day."
The Rapponottis say whoever the thieves are, they can keep everything they took, if they just return Sydney.
"I want my dog back. Just drop the dog off, no questions asked," Mike Rapponotti said.