Lost All Contact On My Nexus 4 Device
Your contacts might have been synced with the old Google account. You can try doing this:


Login on your computer with the old Gmail. Go to "Contacts" and see if you have all your contacts visible over there. ("Contacts" option will be available on top left, where there is a caption of "Gmail" along with an arrow).
If you find your old contacts in the above step, login to your phone with old Gmail Id. You will probably see all your contacts again. 
Export all the contacts to your phone memory.
Login with new Gmail Id.