Chosen Solution
I have a brand new 24" Smart Vizio with the sound at 100% and it is very, very low. The above answers are not helpful.
@helenertd since this is a new TV I would not do anything else but check the sound settings. If those are okay and the sound is still at a low volume, notify the place where you purchased the TV from and arrange for an exchange. Also, let us know what model your new Vizio TV is.