Disclaimer
Cellzio provides a "network search" for mobile phones.
Through Cellzio one can discover where a mobile phone is located worldwide (and probably also the user of this phone). Unfortunately, the service is not always reliable, if the mobile phone is switched off or when the Network provider is not covered by Cellzio, there is no place positioning. You can find the list with network partners here
To be able to do a search you first need to register for the service.