To maintain privacy on internet is bit difficult. But surprisingly, WhatsApp has a feature through which you can send private messages. If you want to send a group message, without letting anyone in the group know who else received that message, and then watching every subsequent response, then the Broadcast feature is there for you. Follow the below steps for this.
a) Open WhatsApp and clcik on the options icon i.e. three dots.
b) Click on New Broadcast.
c) Enter the name of all the contacts, to which you want to send private messages.
d) Click on create, then write your message and sent it across.