Not the anon, but it's really simple. You know who you want to work for. You contact them, and ask how to submit a portfolio for consideration. If you want to do, for example, fantasy novel book covers, you contact all of the fantasy book publishers, ask for the art director/art department, and ask. They won't be mad, it's part of their job. Some of the best advice I got early on was contacting art directors and asking how to sell them art - and if I got them on the phone, I'd ask questions. Most people like talking shop, and if they have a minute, will talk to you.
The most you'll get done with social media is attention/gratification, and private commissions, but if you want to work in the pro space, you have to talk to the people who do the buying. They don't have time for social media, they're busy. You have to set up a portfolio site, send out mailings occasionally with new work, always be pimping your book to everyone. That's what an agent does for you, if you get big enough to need one.
Nobody is gonna come find you. You have to make yourself known.