Are the Apple competitions real or a scam?

Recently when I've been on my iPod on Facebook, if I click on a link to read an article a message will pop up saying something like "Congratulations you've been chosen as a lucky winner for the new iPhone 7!" The message is in a white box and only has one button underneath that says "OK" so if I want to ignore the message I have to go off the app, close it and then go back on.

I've always assumed it was a scam but there's a couple of hints that could mean it's the real deal. Firstly, sometimes the message will say "lucky iPod user" which to me is strange because how would they know that I'm using my iPod? Secondly, it's always Apple products being advertised, so all of these messages have got a common theme of Apple. Thirdly, it's not just one particular link or website link that always means this message turns up e.g. It's not always on websites such as 'diply.com' that this message comes up so it would also be strange if three or four different websites always came up with the same message.

But there are also things that make me hesitant, I've never seen the same 'competition' twice, if you click on the OK button it takes you to a survey-type-website place that I've never seen before and doesn't look like Apple have set it up.

If anyone can shed some light on this that would be fab because let's face it, if I can get a free iPhone, I'm going to do it!

Scams.

They may technically be a competition or draw of some sort, but with eg. One item (supposedly) awarded per year or per million victims. Even that's unlikely.

Things like that are 99% just to persuade people to give up their email addresses and other info, which are extremely valuable to spammers.

Don't even click the OK button.
You don't know what's under that button, you could be giving someone access to your files or letting in a virus.