Does this help too? I don't use messenger, but found this:
Open your device's All Apps menu Apps menu.
Tap the Messenger app Messenger.
At the bottom right, tap Compose .
In the "To" field, enter a name from your contacts or a mobile phone number.
Below the "To" field, you can tap Frequents to choose from frequent contacts, or All contacts to choose from your list of contacts.
To send the message to a group, first add one person and then tap Group Group . You can add more contacts or more mobile phone numbers. If you’re sending a group message, make sure to turn on group messaging in Messenger settings.
If you choose to enter a name or mobile number in the "To" field, matching contacts will appear as you type, if any exist in your contacts. You can touch a suggested recipient or continue entering the phone number.
To write your message, tap the "Send message" box and type.
To save a message as a draft while writing it, tap Back Back . To resume writing that message, tap the conversation.
To send, tap Send Send. If you have more than one SIM card installed in your device, you may need to first choose which SIM card you want to use to send the message.
Source:
https://support.google.com/nexus/answer/6080324
Chris