You can only send messages to your level 1 affiliates. You cannot contact the other levels 2-16. You can however contact your level 1 and ask them to pass on tips and tricks to their level 1 (your level 2).
To contact your level 1 affiliates go to the downline link in the top menu after logging in to your back office and select all my level 1. This will show you everyone you've sponsored directly.
To contact them all you need to do is click their username and visit their profile page. Click the contact button and write your message to the person.
After you send a message, they will see the new message alert appear on the messages menu. Now your level 1 affiliate can reply.
If you want to contact your level 2, ask your level 1 to copy and paste your message.
Why do we do this? Because of data laws and you need permission from your level 1 to contact people they referred.
Get the contact details for your level 1 affiliates - Click here