Depends a lot on your area of interest, but to me Research Gate
(RG) is a good option since you have specialists on almost any science/tech field, from the academy as well from the industry. You can make questions (like a forum), download technical papers, and contact people. I've used RG for plasma physics/applications and biomedical engineering.
Also try professional associations, just like Joanan Hernandez mentioned IEEE, ASME, ASQ, etc.