In my exploration of effective platforms for promoting a new app, I've found that several online forums stand out. Tech-based forums like TechCrunch, Product Hunt, and Hacker News are top picks as they attract tech-savvy audiences who are always on the lookout for new apps. Reddit also offers various subreddits where developers can introduce their new apps. Quora, with its high-quality engagement, is another great space to get the word out. Lastly, social media platforms like Facebook groups dedicated to app promotion can be very useful too.