While not specifically about ecommerce, r/smallbusiness is a great place to ask questions and learn from others who are starting, owning and growing a small business.
If you're new to the ecommerce game and just about to make the plunge, Shopify Newbies is a strong group with close to 100,000 members that can help you get started on your Shopify ecommerce business journey.
The definitive r/Marketing community on Reddit, where you can connect with marketing + advertising industry professionals to discuss marketing strategy, media planning, digital, social, search,, email, content, copywriting, segmentation, attribution and more.
Welcome to the Ecom Queens Community, with 50,000 creative eCommerce entrepreneurs including Etsy Sellers, Shopify website owners, and business owners on many other platforms and marketplaces.
EcomHub's official Facebook group is for high-level discussions and all things Amazon FBA & eCommerce strategies.
Richard Lazazzera of A Better Lemonade Stand runs Ecommerce Entrepreneurs. With close to 50,000 members, the Facebook group is one of the largest forums for discussion, learning, and growth on Shopify, ecommerce, digital marketing, Adwords, SEO, SEM, web analytics, content, CRM, etc.