For background, please see: Changes - July 2018
In all probability, if you get no results for your search, it is because you are searching for a complete or partial address, rather than a place name.
For example, "10 Downing Street, London" gives no results (addresses are no longer supported in the search function, due to Google's price hikes). "Westminster, London" does give a result (place names are supported).
The mobile app versions of TPE are unaffected by the current limitations in the web app search capability. TPE for iOS uses Apple's geocoding service together with Geonames. TPE for Android uses a combination of other third party services (see here for details).
Nov 2019: we're in the process of redeveloping the web app and as part of this project, a new search back-end will be incorporated (already developed and in use in our Android app). We don't have a launch date to announce at present, but we hope to make quick progress towards completion.