Nevarez, a Vietnam War veteran who served as a Navy Seabee, is diabetic and Chulo helps monitor his blood sugar level.
"When he sees me feel bad and he starts barking, that means I need to take my insulin shot," Nevarez told NBC News.
Nevarez is asking for whoever took Chulo to return him. He is even offering a $2,000 reward, money he planned to pay his rent with, according to WABC.
"I just want my dog back. I can't sleep without him, and I don't feel good," Nevarez told NBC News.