Growing your follower base on social media is important as it gives you more people to speak to about your products. Think of each new follower as a potential customer - how would you talk to a customer if they wandered into your brick-and-mortar store?
Each platform is different. On Twitter you can send a personalised message to any new followers (make sure they are a real person by checking out their profile beforehand.) Don’t automate this, make it genuine and be interested in that person!
For example, if you were a shoe store you might tweet something like this:
‘Hey @TwitterName, thanks for following us. We love the red outfit in your profile picture, let us know if you need any help picking out your dream pair of shoes to go with it’
You can also direct message your followers on Instagram in a similar way!