The first issue I see is you don't explain on the first page what it is you actually do. Without a clear message, people will just leave a site. Even after reading the About page, I'm not quite sure. It's a marketplace for NPOs to buy discounted things? If so, you need to say that in a more elegant way on the main page and any other landing page.
The menu navigation links are way too small too, good luck hitting the right one on a touchscreen. 44px is the recommended minimum height for buttons and such like. Also, 'Discuss' as a nav link doesn't tell me where I'm going when I click that link. Just label it 'Forum' so people know.
Overall it just doesn't look trustworthy. You've only got a few seconds (if that!) to make a good impression.
@Paul Murray and @Levi - I've been struggling to figure out how to concisely explain what we are up to, which is why I have the three buttons (for businesses, individuals, non-profits), but I haven't created content for them yet. I'm thinking most peoples first stop (at least where I'd direct people) is to the appropriate "landing page" - which would be one of those three...
I'll take a look at the icon sizes and I'm thinking about removing the forums altogether till the site gets some traction.
@Levi - Can you tell me what seems to be broken on mobile? And what device you are using? I've been reviewing on various mobile viewports and using my own Google Pixel 2.
Like the others have suggested, it’s not at all clear what the site is about.
Forget about the design of the site for now a focus on getting the content written. That will maybe help you get a bit of direction.
It does look like it’s going to be some sort of directory. If that is the case you are going to struggle to get any sort of traction. People rarely use directories for anything any more, there are too many other very efficient ways of finding goods and services.