I did a quick Google search for you. Here's an excerpt from the well-known fatwa site islamqa.com :
The Committee replied: This kind of dealing is haraam, because the purpose of this dealing is to earn commission, not to buy the product. The commission may reach tens of thousands, whilst the product is not worth more than a few hundred. Any smart person who is offered a choice between the two will choose the commission. Hence these companies rely on marketing and advertising of their product which emphasizes the size of the large commission which the participant can earn, and offers the incentive of a large profit in return for a small sum, which is the price of the product. The product marketed by such companies is merely a screen or a means of earning these commissions and profits.
The Committee replied: This kind of dealing is haraam, because the purpose of this dealing is to earn commission, not to buy the product. The commission may reach tens of thousands, whilst the product is not worth more than a few hundred. Any smart person who is offered a choice between the two will choose the commission. Hence these companies rely on marketing and advertising of their product which emphasizes the size of the large commission which the participant can earn, and offers the incentive of a large profit in return for a small sum, which is the price of the product. The product marketed by such companies is merely a screen or a means of earning these commissions and profits.
The rest of the answer can be found here
