Offer your loyal customers something – perhaps a goodie, a surprise.
The more your loyal followers will speak about you, better your word to mouth publicity will get and their followers will become your prospect.
Consider a lifetime value of a customer as well as the size of their network – as the benchmark / critical metric for your marketing / targeting efforts.
A customer ( for e.g.: flyer ) at 27 is definitely going to use more services ( for e.g.: travel ) every year – possibly more than the previous year. Therefore it is prudent to identify personas of your customers and offer different packages / surprises to them so that they just won’t stop speaking about you.
The impressions they will fetch for you in yours / their posts will mostly exceed the amount of impressions the brand gets by itself.
Since social media is all about community, it is the people / followers who makes the brand stronger or weak.