Some devices, including Sonos and Belkin WeMo, don't provide cloud access to your devices. Instead, we discover and control them through your local network. This discovery process can sometimes be a little inconsistent depending on your network setup.
The most common issue we encounter is that people simply aren't on the same wireless network as the device they're trying to find. Make sure that you're connected to the same network that you use to control your Sonos devices.
Once connected, try repeating the discovery process. For iOS, tap the magnifying glass icon on the Things tab. For Android, open the nav drawer, and tap "Find New Devices".
If they still aren't discovered, please contact support. Be sure to include details about your Sonos setup, like how many speakers you have, how they're connected (wi-fi, ethernet, or with a Sonos Bridge or Boost.)