This is a great read from Chartboost... When you understand that some of these "Youtube Influencers" have more viewing figures than your favourite TV network, you might want to consider partnering up on your next app launch How to Grow a Mobile Game Through Influencers.
I guess it all depends on the level of traffic they deliver, as to whether they are expensive or not. If they drive a few hundred thousand eyeballs towards your app, then this could be extremely cost-effective.
The biggest advantage of influencers is that they don't show explicit ads like "click to install" or force users to install. they show the game/app, and the users who are interesed will install it, the retention rate is higher in this case.
The big ones are for sure very interesting. As are Twitter celebrities, Vine stars and others. Be careful though with fake accounts. There are a lot of youtubers with fake followers and fake views. It exists as well on Twitter, Facebook and Instagram. Just research them a little and see if there is a real and active community involved. If yes, then something like that could be a gold mine. Big Youtubers are mostly interested in console/pc games and not as much in mobile games.
Also many gaming YouTubers (including the biggest "Pewdiepie") host competitions monthly for users to sometimes submit their original games for them to play on their channel. Information about these competitions are usually on their personal websites so check them out!
But those fake downloads and review are everywhere, the whole online marketing is full of with that. The so called app marketing companies are doing that too. Then they provide downloads and reviews agreed in the contract and you will get no organic installs because no real person knows your game...
