Chirag, Once the invitations to the app are out of date, there is no other way to invite to Facebook if you do not allow users to use the FB timeline using tracking / attribution links.
As an application developer, you should also use popular messaging apps and other social networks to use apps like Whatsapp, Kik, Twitter, Kakao, etc. More here
(Disclaimer: I am the founder of GetSocial)
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