At one point the Verizon Message+ app was able to receive and send text messages over Wi-Fi. This capability is purposely disables when used on smartphones that you have a paid cellular service on Verizon with. All other devices have it enabled unless you have the Advanced Calling Service with a smartwatch service.
From the official app description:
Calling: Advanced Calling customers (eligibility rules apply) can link their phone number to the Verizon Messages app on their tablet or compatible smart watch and make and receive calls wherever they want on any network (cellular or Wi-Fi).
I work in a building where no Verizon services exists, but I still need to receive and send texts. Does anyone have a recommended app for texting over Wi-Fi that I can switch to?
Message+ does work when you are on wifi. I do this all the time.
Can I send messages with Verizon Messages over a Wi-Fi network only?
Yes, you can send messages over Wi-Fi only without a mobile network connection from your device. Messages sent and received using Verizon Messages over Wi-Fi will count towards your smartphone's messaging plan.
It it is possible your work wifi is blocking the needed ports for the service to work.
Understanding the VZWmess+ app is the best way to message with no signal over wifi in a VZW customer's case as any other messaging app will require both you and the other person have the same app, unless you use Hangouts, which has SMS (text) integration and will work even if the other person doesn't use Hangouts, plus it is already installed on Androids.
Unfortunately, both are to be removed from further gapps packages as it pertains to OEM versions. Google will give the option for manufacturers to keep the 2 apps, but the 2 have always been (and similar G apps before them) competition for stock message systems.