An internal community is a closed community used to help people in an organization communicate and collaborate.
The community will typically have a specific purpose within an organization. It could be to connect people within a team or department, or it could be to organize projects.
IBMs CSR Influencers Network is a group of IBM employees dedicated to making a social impact. The community helps people organize activities and also helps new people get involved in these programs.
The first step is to decide what you will use your community for. Having a tangible goal will be central to the success of your internal community. Then you can then choose a platform with features that suit your needs.
The good news is that internal communities are often easier to grow than external ones as you already have a group of people to invite.