The problem may be that every "hobby investor" is using some site already. There are communities on those other sites, some of them very old indeed, and those communities may be pretty sticky.

Generic advice:

Stop talking to bloggers, sites, writers. Those people are useless by themselves, as you have now discovered. PR can bring people in, but it can't make them stick.

Talk to some hobby investors. Find some online forum full of them and beg some of them to come and give you some feedback.

What site all those folks using now? What do they hate about that site, and can you fix it on yours?

I was going to suggest that you build something that would draw people in, like a fantasy-trading game... but a quick Google convinces me that the market for that particular idea may be totally saturated.

I don't really agree with bloggers and writers being useless. That's how the word spreads about websites; except for viral means. The article on Lifehacker alone practically doubled my user registrations (about 20% of the total traffic from the article registered).

On the other hand, if you built a couple of desirable new features that test well with samples of your target market and then prod the publicity machine with your new and improved version 2.0, it might work better.

Of course, here we recognize why the app universe is filled with colossal apps full of trendy social features: adding one feature after another is the simplest way to get a series of marketing hooks. If you're pledged to minimalism life is more difficult. Try subtle changes in the defaults or the styling. Try building two versions: the elegant and the feature-gaudy. Try to add just one new feature, but make it so awesome that everyone wants to try it at least once. Build a second, slightly related app that helps drive traffic to the first.

My initial reaction to your site (this time around, I couldn't really make much sense of it before) is that it likely just isn't sticky enough. Though I agree that the 'communities' are way over done, you've included a sign-up to customize option, so you are gathering user details. Your site has the opportunity to serve users who have signed up, and those who have not. You don't have to be a social network to be a community, but I think you should be leveraging the 'community' that you have. For instance - when I come to your site now, it offers me the opportunity to sign-up, or to click on one of the above icons. Wouldn't your site be stickier if when I first come to the site it tells me what you suspect I am looking for? I'm not much of an investor, but your users should be, therefore I should be able to come to your site and be shown a few things that the community is currently finding interesting. Everybody benefits from that kind of stuff- new users and return visitors.

As I see it now, i can get quotes and news from a number of sites. But if you were to aggregate into a popularity list somehow (it can be done!), or recent activity, etc. that might bring people back to your site more often. Doesn't have to be a social network, but even the news sites show you stuff they think you'd be interested in right off the bat. Right now I go to your site and i have to decide what I want to look at. You're probably loosing people right there.