The one I tend to frequent is Britmodeller:
https://www.britmodeller.com/forums/index.php
Various modelling genres with different discussion areas, work-in-progress and completed model pages, buying/selling/bargain areas, rumours, chat, reviews, walkarounds and manufacturer/shop zones. Plenty there for everyone really.
A few others to consider are:
The Airfix Tribute Forum:
https://www.tapatalk.com/groups/airfixtributeforum/
Not just Airfix but does have a lot of good information on what people call the 'Classic British Kit' manufacturers of Airfix, Frog and Matchbox.
Hyperscale:
http://www.hyperscale.com/
More than just a forum. Brett Green is a great modeller and he does plenty of builds and reviews of kits. Has articles, galleries and walkarounds as well. Aircraft and armour are the focus here though.
These are just a starting point and should keep you going for a while.
HTH,
John.