Great question. I believe it really comes down to two pieces of criteria.
- Who (as in what segment) is your customer?
- What is the purpose of the communication?
If your customer is the general public you may want to make more general announcements. However, it is unlikely that the general public as a whole is your customer. Perhaps if you are a giant big box chain, but even then it is unlikely. You would typically have customer segments, potentially stratified by the range of your products or services or the prices of your goods.
Getting the attention of the general public is not easy because the message must resound with everyone (not very likely). Chances are you need to focus your communication to your largest or most profitable customer segments (e.g. use social networks that the custom segment uses to send them a focused message).
The purpose of the communication will also help you focus your communication.
- Are you trying to get customers who have previously made a purchase to make another purchase?
- Are you trying to reward your loyal customers?
- Are you trying to get new customers?
- Are you announcing a new product/service or an update?
- Are you venturing into a new industry or demographic?
All of the above questions will help you focus your communication. Why focus? Using focused communication will produce a better response from customers (you are calling them to act on something). Using focused communication makes the message more personal.
"The general public" cannot realistically, commercially of culturally be considered a target market (or as customers).
All media (social or otherwise), claiming to be for the general public, is by its very definition far from focused. You can only ever focus on customers, a microcosm of a specific section of the general public.