Doing multiple pushups helps lose man boobs?

No: Gynecomastia (aka man boobs) are accumulation of breast tissue in men. They are not a function of fat and working out your pectoral muscles will not eliminate them. If you truly have gynecomastia, it will need to be corrected by a plastic surgeon once the underlying causes have been ruled out.

Can't hurt: "man boobs", or gynecomastia, are usually due to a combination of glandular tissue and fat. Of the two, fat contributes far more to the problem in most cases. The muscles that grow due to pushups are buried beneath those layers and are usually hidden as a result. On the other hand, exercise of any sort reduces fat throughout the body and may therefore be of indirect benefit.