I'm fairly certain that all Roku TVs support Roku voice remotes; certainly any new TV. You should see "Add a new remote" under Settings->Remotes & devices->Remotes. Keep in mind that the remote won't work right out of the box - it has to be paired. Follow the instructions after you select the "Add a new remote" option.
As for the app not seeing your TV, the phone and the TV have to be connected to the same network. You probably already know that, but I thought I should throw that out there just in case.
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