Make no mistake, YouTube is an entire side industry to Hollywood and much bigger than the traditional mediums of television and movie. Companies devoted solely to producing YouTube vids and trying to make viral videos - have a friend who has worked for a couple of them over in LA and even 1 million views for a video is a huge deal. It's definitely an exploitable industry and does happen. YouTube have complete control over top search matches and order displayed content, featured content etc. No doubt there's a pay off for investing in buying likes and views, but nowhere near striking it lucky with a niche that spreads like word of mouth.
A lot of those kids have had producers approach them and offer to manage etc., some of them have got where they are by having people invest in their character/personality.
Bieber is a good example - started uploading cover vids, got heaps of views, music producers took notice and got on board to invest in him.