To add my own: I've received one, maybe two spam SMS messages in my entire life, none at all in the last few years. I have received one or two spam messages in WhatsApp.
Facebook Messenger is pretty spammy for me, as is Twitter DMs.
Ok but I was talking about dedicated messenger apps, not the messaging feature of what are basically social media apps. Those are all full of spam if you've got enough contacts and liked enough things.