1. Use a newsletter platform that has inbuilt growth loops and network effects. E.g. Substack, Beehiiv. They have features like recommendations, pop-ups, and referrals that make it a lot easier for you to grow your newsletter organically. Personally, I use
Substack.
2. Create a content distribution plan. Look for communities where your target audience is (e.g. founder communities, Indiehackers, relevant sub-Reddits, Quora, etc.) and post your content there. Use your content to answer questions where relevant.
3. Leverage co-creation and other people's networks. Should be a lot easier for you since you're telling the stories of startups and founders. Get those founders (or their startup's social media team) to post about your content when you feature them. That way, you're getting a foot into their own audience as well.
4. Repurpose or extend your content. E.g. if a particular founder success story is gaining traction, host an AMA session where readers (and the general public) can ask the founder more questions live.