Using social media is a great way for marketers to enrich their contact list. One thing you can do is encourage your social media followers to join your email list by launching a contest. For example, announce that you will be holding a draw for a special gift among all of your email subscribers at the end of each month, or among subscribers who have signed up within a certain period.

Photo contests, selfie contests, essay contests, caption contests or video contests are many contest ideas that you can try out. But make sure there’s a direct link between the competition and your newsletter content so that subscribers don’t unsubscribe from your communications once they have received their special gift. You need to make them want to stick around for more.
There are few things to keep in mind when launching a competition on your social networks:
Result
Social media contests build an incentive for users to become part of your email list and, with a good email strategy, will lead to engaged subscribers.