People are losing money from the hands of these scammers on daily basis. they do not have any particular investment that is bringing the profit. what they do is taking money from the new investors and pay the Old investors. it is not reliable.I have read many negative reviews about HYIP sites , and I can say that it is attributed to the fact that they operate through ponzi scheme.
That is , they collect from Peter to pay Paul , and once there is no Peter depositing , Paul can't be paid.
Few HYIP sites that closes is never becomes they want to scam people , some are as a result of Withdrawal request greater than deposit.
Thus , hyip sites can be long lasting if they can invest in a business that will be yielding money. For example , a hyip that will pay in a week intervals can put the money into business that Involves daily sales . At the end of the week ,they collect their own profit and pay back the users share . With this , hyip sites can be sustained.