It sounds like a compatibility issue, but the volumio image is created for all versions of the pi with the exception of the 3B.
You can use either a ping to ‘volumio’ (without the quotes) on your local network or try to browse to volumio.local with your browser.
If all else fails you could log into your router (or other DHCP server) to check if any IP was assigned to a host with volumio in the name.
Are you also absolutely sure it’s a Rasperry Pi B+? Could you post a picture of the top of the Pi? With the revision number on it.
I have tried Volumio on a B, B+ and 2B, all without problems.