If you need validation, the quick way is to setup some adverts. Google, Facebook, Twitter, etc. Or find a place where you can spread your pitch and link. You should have some kind of validation goal, like email signup or trial download or something.

Product Hunt is a good place or maybe some beta sites like BetaList to get started.

The longer and "cheaper" way is to write your own content, which gets attention. It depends on how connected you are already. Some people have already a huge interested audience.

Self-promotion. If I had such a project I'd be adding a little link to it here, and talking about how awesome it was..

But you need to either build an audience, pay for adverts and be optimistic, or be constantly promoting it in all appropriate venues. Having google-alerts, and twitter-searches, to make sure you can join suitable threads promptly is very useful too.

Before launching a product, I followed the advice to build up an audience first. For instance, having a website, that is somehow in the context of the product, and write about the topic constantly. Afterward you can redirect the audience to your product.