IP address won't cut it. That is assigned on each network, and sometimes varies within the same network, depending on the network configuration. What you're looking for is the MAC address.
If you have the serial number of the Roku TV, file a police report, and they should get notified if someone pawns it, or if it's otherwise recovered in an action.
Apart from that, it'll be nearly impossible to locate. I don't know if Roku can disable the device based on MAC address or serial number. Even if they could, they'd need a whole bunch of proof it's your device, to include a police report.
If they do a factory reset of the Roku TV, it will come out of Guest Mode. I wish I could give you better news.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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