Resolution: To initiate contact with a single recipient, follow the steps below:
Single Recipient
1) To initiate contact with another user, click on the button in the top left corner of Microsoft Teams, above your contact list.

2) Then, in the window that appears, begin typing the recipient's name or email address.

3) Once you see the user's name appear, simply click on their name and you'll be able to begin a conversation by typing your message in the bottom of the screen.
Multiple Recipients
1) To initiate contact with multiple users, begin by adding an initial response, as described above.
2) After selecting the first recipient, continue typing in the next users name in the same bar

3) You can do this with as many recipients as you wish
4) From there, simply begin typing your message in the box at the bottom