- Open your Google+ home screen
- Head to the “Circle” tab
- Click “Add a new person”
- Write down their email (preferably Google account), or maybe you can try emails from other domains
- Pick the proper circle for your friend
- Head back to the home screen, then write your friend’s email on the stream
There’s another alternative if you want to sent all-at-once invitation, just repeat the step 1-5. Then you can sent the invitation to the circle instead of writing down the emails one by one.