This is a Ponzi scheme.

A Ponzi scheme is a system in which earlier investors are paid with the investments of later ones.  Therefore it relies on a constantly increasing stream of new investors until the admin feels that they can make a good profit, at which point they run off and steal the investors' money.

Actually, this kind of Ponzi scheme is a lot more like Bitminer.io in which they never paid in the first place and are most likely a straight up scam.  The way that Bitminer.io did it is that they offer a free service in which you can only actually withdraw at a high amount and when you try to do it it says to wait up to thirty days, and in the meantime to pay for instant withdrawals and a better service.  They never intended to pay you for the free service, but since you now think they're legit because of the balance it built up, you put in money, which they steal.

They might even selectively pay monitors of these sites and other people which they believe will get them good publicity in a ruse to scams thousands more naive investors into the system.

Don't put any money in, and get away from that site straight away.  No one is going to give you free money unless they're actually interested in you individually, so don't believe it until it happens.