My male pug is 4 months .he wont eat. he hasnt ate anything for nearly 16 hours. any advice.?

Lately (over the past few days his appetite has slowed down, but he was eating. but today he wont touch his food. I put 2 plates down with 2 different foods that he is use to..hes not playing either. When I sweep the floor he usually chases the broom,but didnt move at all today. Hes not vomiting. Ay advice would help. How long before its too long for him not to eat.