https://www.quora.com/What-are-key-strategies-to-acquire-first-100K-users-with-zero-marketing-budget

Best answer:

#1 Make a great product but y'all know that so I'll just dive into the tactics#2 Create your target marketing sheet. See this: Quant Based Marketing for Start Ups#3 Partner with similar companies and create benefit for them to email their free users#4 Reach out to offline Meetup groups who generally have 200-1,000 person mailing lists#5 Befriend owners of Facebook pages and see if you can do contests for an in-kind trade#6 Go to the /subreddit (Page on Reddit) related to your business and leave comments#7 Search 5-10 keywords related to you on Google and leave comments on those related pages. #8 Give away free content or ask partners (like I did with My Travel Hacks & Free Luggage for Your Next Adventure (Part 2))#9 Go write guest posts for any site that's related. Use Technorati or ask your existing customers which sites they like to go to.#10 Email the existing users you have asking for them to refer other people. This sounds obvious but hardly ANYONE does it. It helps if your product doesn't suck ass.#11 Leave video responses on popular-related YouTube Videos#12 Manually reach out and connect with your first 1000 customers. More likely they are MORE important than then 99,000 next people you'll get#13 Raise your prices so you don't need to get so many people :)#14 Manually reach out to Twitter / Facebook followers of your competitors#15 Look at new channels that have less competition (rules) like snapchat, pinterest, instagram to drive traffic#16 Consider going international where traffic is cheaper (okay, you're not paying but you know what I'm saying)#17 Evaluate doing mobile related marketing since it's more affordable (less competition)#18 Get your site featured on http://AppSumo.com, DailyWorth.com, Thrillist, DailyCandy, Groupon or some site that promotes others. I've done this 3 times with http://mint.com, http://v11media.com and http://appsumo.com