If I send a message to all my friends on facebook, will it be a group message?

[pri✍]

If the "To:" is to only one person, it's not; if you put all your friends name in one "To:", then it's a group message.
If you want to send the dame message to all your friend, why don't you just post it in your timeline with the audience set to Friends?
Sending one by one message to all your friends, might be considered as spam by FB that might put you into jail, block from sending message.