Every "first 100 users" article you've read was written by someone who already had 50,000 Twitter followers. This one isn't. The first 100 users come from one source: you, manually, one at a time, for six weeks. There is no shortcut and you don't need one.
Step 1: Define the user so narrowly your friends laugh
"Solo bookkeepers in the US who serve 5–15 SMB clients and use QuickBooks Online." That's a user. "Small business owners" isn't. See Niche Down or Die.
Step 2: Find where 1,000 of them already gather
One subreddit. One Slack group. One Facebook group. One annual conference. One trade publication. You only need one watering hole, not ten. Spend a week lurking before you post.
Step 3: Show up as a contributor for 14 days first
Answer questions. Share resources. Don't mention your product. You're depositing trust into an account you'll later withdraw from. If you skip this step, your launch post gets deleted.
Step 4: 30 cold DMs per day, but not as a pitch
The script: "Hey — I'm researching how [specific role] handles [specific workflow]. Could I ask you 3 questions? Not selling anything." Even a 5% response rate gives you 1.5 calls a day. See Cold Outreach for Validation.
Step 5: Convert calls into beta users
After every call, end with: "I'm building something for exactly this. Would you want early access for free in exchange for honest feedback?" Conversion rate is typically 30–50%.
Step 6: Ask each beta user for one referral
"Who's the one other person you know who has this problem worse than you?" Compounds ferociously. Half your first 100 will come this way.
Step 7: Write one cornerstone piece for SEO
While the manual outreach runs, publish one deep piece on the exact long-tail keyword your users search. It won't help in week 1. By month 6 it's a quarter of your signups.
The math
30 DMs/day × 5% response × 5 days/week = 7.5 conversations/week. At 40% conversion to beta, that's 3 users/week. 100 users in ~33 weeks of focused work. Most founders quit at week 8.