Sponsored FB Comps

redfox5

When I'm on FB on my phone, I get loads of sponsored comps come up, which can be entered really quickly on my phone. 
When I jump on my PC and try and find these comps using either the company's official FB page or website so I can share them on here, I can rarely find them. 
Does anyone else have this issue? 
For example, I've just entered one for TNC Drinks (The Naked Collective) which said that if you sign up to newsletter, you will be entered into a comp to win a sample drink. I've done this and got an email come through confirming but it doesn't say anything on their official site about this when you sign up.  But they are official advertisements. 

libra10

I've found this when using my laptop.  Have tried right-clicking the sponsored item, but when checking their webpage there's nothing there!
Not sure how they're generated, and have wondered whether they're genuine.