I think that a social media platform based on the blockchain might have some level of success.Perhaps the blockchain technology might cause Facebook,Youtube and Twitter to die in the future.A search engine is just a bunch of web crawl bots,that index web pages and rank them using Google`s secret ranking algorithms.Social networks work in a completely different way and the blockchain might be more suitable for them.
What is the common linkage between blockchain and social networking sites as well as youtube, they have a sustainable business model and nothing is going to stop them, block chain can be used to build several systems but it cannot replace the social networking sites, there might be better version and people might switch them to those but blockchain does not have anything to play with social media and search engines.