I think the answer heavily depends on how confident you are in yourself. Do you feel your success was a fluke, or could you mimic it with something else? Having 24K in capital is great, but if you know anything about the tech startup space you'll know it's no sure ticket to riches. You need to board a train that can take you higher, and that either means something you do yourself or tagging along with someone else. Both are uncertain roads, so my best advice is to research and weigh your decisions carefully. You might come back and ask HN a 'Should I invest money in this?' question.
I'm pretty smart, but you still need a confluence of certain things at a certain time, which was clearly the case with the app store about 8 months ago, and which I took advantage of.
One can never know if everything will fall perfectly in place the next time.
Something I'd actually seriously consider in your place is YC companies. They get around 20K which is just enough to create a prototype/beta to solicit a larger round. This is not very much and I imagine many don't raise money right away after their Demo Day. Having another 15-20K could be highly desired in these earliest days. YC has already placed their bets that these companies will become great, and I think their portfolio could have a 40% or better success rate (provided timely variables fit together). If you could add your money and app expertise to make a YC (or another) company stronger, that might be the best risk to reward ratio you can have.
You might be surprised at the responses you'd get. As you probably know web startups are cheaper than ever to build; that's why the YC model works so well. It's not in a startup's interest to raise huge amounts and give up lots of equity early on; it's far better to give up less than 10% (YC typically gets 6-7%). If you saw a company that you could relate to, and which you understood the dynamics of, and furthermore might also be able to contribute your support to then that can be worth quite a lot. The money is just part of what you can bring to the table. You've already built a successful tech app so you obviously have some tech knowledge, which is likely valuable. It certainly doesn't hurt to ask; the YC companies are the same types likely to be on HN, so approach it as more of a community/team aspect than a rigid VC offer. An early YC company might give up another 4-5% for what you could offer, and even that small amount might be worth millions in the not-too-distant future - meeting your criteria.
