Although I am unsure what your laws are, what we do is place an expiration date on the renewal offer. If that date rolls by without any acknowledgement from the resident, and calls go unanswered and emails are ignored, then we place a notice and certify mail a notice to the resident that their apartment will be placed on NOTICE status by Day X, 2018. Then we do just that. Because our units rent sight unseen 90% of the time because of our online only leasing process, many times the apartment is quickly re-rented. It's a difficult life lesson to find out you have to move because you paid no attention to your responsibility to keep the Office team informed, and of course, it can wreak havoc when this happens and the resident asks to stay, but consequences teach us, don't they? If this is not permissible in your state, then I honestly don't know what to do, other than tie big bouquets of balloons to the resident's door with a note saying, Renew or Move!
I know the laws vary from state to state, but in NC - we have a clause in our lease if it's not renewed, they revert to a month-to-month lease, which increases their monthly rent by $100.