Everyone wants a marketing silver bullet or an advertising secret potion. Unfortunately, those things don't exist.
However, there are a few ways you can generate a solid amount of attention and engagement online without spending much money. Will these still be relevant in six months? Who knows. We live in a time of disappearing photos being worth billions of dollars. For right now, though, these work and can be extremely effective.
1. Product Hunt (free) http://producthunt.co
If you haven't checked out Product Hunt yet, you're welcome. It's basically the cool kids' table from the high school cafeteria reincarnate. Except, instead of jocks, you'll find a bunch of geeks and nerds creating really cool products (apps, books, subscription services, webtools, etc.). I'm a self-proclaimed geek, so I hope no offense is taken.
It's 100 percent free to sign up and to submit your "product." This article does a great job of showcasing how to interact with the Product Hunt community to get some additional traction.
2. Subreddits (free, with a caveat) http://redditlist.com
Reddit is kind of like the pulse of the internet. The main page features the most popular stuff, but much of that stuff is found in separate subcategories called subreddits. Don't think there's a subreddit for you or your business? I highly doubt that.
Not only is there a sizable community just for startups and entrepreneurs, but there are also subreddits for such things as surfing, comics, gadgets, Star Wars, health, and "explain like I'm five."
The caveat to Reddit is that you're bound to get lots of feedback if you share content on it. Sometimes that feedback can be awesome, but sometimes it can be a bunch of criticism too. The key to sharing content anywhere on Reddit is to provide value and not just ask for people to check out your stuff.
3. Facebook ads (paid)
Gone are the days you can create a Facebook page, get a ton of Fans/Likes, and then promote content to your audience with expectations of organic engagement and sales. That was Facebook in 2010. If you're using Facebook nowadays, realize it's a paid advertising platform and embrace that. And I'm not talking about "Boosted" or "Promoted" posts.
Facebook ads are incredibly cheap to set up, but can take some work and experience to manage. If you aren't familiar, I highly recommend hiring a Facebook ads expert. The best way to find one is to contact business owners you might know whose ads pop up in your Facebook newsfeed. Be forewarned, there are a ton of variables involved with Facebook ads, and lots of iterations and testing are required (luckily, this can be done inexpensively).
One additional feature of Facebook ads for existing page owners/managers is what's called "Facebook Dark Posts." Essentially these are standard posts you'd write for your page, but they only get shown as ads in newsfeeds. Crazy, huh?
Like anything with Facebook, the effectiveness and affordability of its advertising will last only so long. Now is a really good time to get on board.
4. HackerNews (free) https://news.ycombinator.com
Very similar to Product Hunt, but much harder to get traction, as it's been around a bit longer. With a creative submission, you can definitely generate some traffic and buzz on HackerNews. Be warned, it's not the sexiest of interfaces and the popular content skews heavily toward tech-related stuff.
5. Your contact list (free)
Imagine a social network where all your "status updates" get read. Where you get feedback on everything you "post." Where you've built trust for years and are guaranteed a response or helping hand.
Yep, that's your existing contact list; a heavily overlooked and ignored network of people.
For years you've built relationships, nurtured them, and created trust, and yet you don't run to these people when you want to promote your new awesome thing. These should be the people you go to first so you can get critical feedback and avoiding marketing a product that isn't quite ready for the masses. You'd rather show 10 friends your business and have them spot errors than let thousands of people visit your site and have a bad first experience right? The answer should be yes!
Don't spam your contacts though. Treat these folks with extra special care. Oh, and don't forget to use follow-up emails when reaching out to your contacts.
As a friendly reminder, none of these things are going to make or break your business. They might help you break out, but you certainly need to keep marketing your business and doing creative things to attract and retain customers.
Good luck and happy promoting!