You put some bait (let's say promise of valuable freemium product, e.g. a pdf with some guide) and a user gives their personal email to your mailing database where that product will be delivered.
This is based on the hope that the user will later forget to unsubscribe from that mailing database.
My community is based on users who do not use email but they use Facebook. How to implement a similar userbase-building technique on Facebook?
I can do it manually via something like posting this "Like this post/video to get free guide how to..." but I'd like some more sophisticated way.