I mean, we're practically all advertisers in some way or another - every time we share a promotion with our friends, or even just discuss a new product we're interested in. Most of the time we're not advertising for the sake of profit, but just sharing interests with like-minded people.
Social media outlets attempt to tap into our general ignorance of advertising profitability - and they act as the middle-man between companies wishing to advertise, and the people who're sharing with friends - but facebook take all of the profit by inserting themselves between these relationships, and the users who are sharing don't notice they done a large part of the advertising work, for free.
Facebook can obviously provide some usefulness, because it knows where you are, what your interests are, and your recent activities - so it can target you for specific promotions. A recent video by Vertitasium[1] showed how this isn't without problems though, and does not directly correspond to ROI for advertisers. (Likewise with many advertising models, there's always people trying to game them to earn a quick buck). Facebook provide the "advertising seed", by predicting who is likely to share.
I see a different potential model that could arise with the gaining popularity of cryptocurrencies and electronic transactions though - one where advertisers only pay when it results in a direct ROI, by tracing electronic signatures through a public, distributed ledger.
If a company wants to promote a product, and they offer a $10 advertising bounty for every advertisement which results in a direct sale. They initially create two digital signatures using "cryptocurrency X" and pass them to advertising agencies A and B. A advertises the product with "Get $5 back off your purchase when you register your product using X", in which they make this guarantee by creating a transaction whereby the original input transaction from the company is used as the input, and the output is split in half between the buyer and A. When the buyer then registers their product with the advertising company, they release the $10 into the public ledger, which propagates $5 to A, and $5 back to the buyer. B is greedy and wants all of the $10 for themselves, but fails to make any direct sale, and thus, is not paid anything.
In this way, there can be any number of middle-men between the company and the buyer, and each party can agree on the fees they wish to have for each direct sale that results. By having a public ledger of who is making the sales, companies and advertisers alike can use analytics to discover the best routes to sales, and narrow down their advertising strategies, and agree on the most reasonable fees for each of the parties involved.
The social media aspect is to have this technology encoded into the social platform, such that it is mostly invisible to users - they simply "promote" an existing post which has a bounty attached to it, and if those re-posts eventually result in direct sales, their wallet starts to grow. The part where users need to actively know about the system is when they purchase and register their purchase, such as to trigger the release of the advertising fees through the chain in the public ledger.
These are only rough ideas and I have no idea how they'd be implemented effectively, including issues around anonymity and ensuring the system cannot be gamed by registering a product then returning it, for example, but I think there's infinite potential for such ideas to replace the advertising empires - so that literally anyone can become a paid-advertiser, and where ones effectiveness as an advertiser results in profit. This wouldn't make facebook et al obsolete, only distribute the profit a bit more - and it would help to improve the AI which is behind FB's advertising, as it would be inefficient to promote things which aren't likely to result in direct sales. Everyone wins, although facebook's profits may decline a bit.
[1]:https://www.youtube.com/watch?v=oVfHeWTKjag, also https://www.youtube.com/watch?v=l9ZqXlHl65g