The Furby 2012 app is available for iOS and Android devices, and is on both store pages under "Furby" by Hasbro Inc. The new Furby Boom has its own app under "Furby Boom," and it is not compatible with the Furby 2012.
The lack of sound is most likely the result of a loose speaker membrane. It can be remedied by pressing something against the speaker membrane to hold it in. It is also possible that the speaker may be broken, in which case the speaker should be completely replaced.
Furbies communicate with high pitched sound waves that aren't audible to most people. This communication is very sensitive and will be difficult to pick up by the Furby microphone if there is any background noise. Try putting the Furbies somewhere with less background noise and this should fix the problem.