There were apps like this among Facebook friends, I don't think something like this would pickup because you need to know about the app.

Women are showered with people approaching them so they don't feel the need to register - or they register to something more on-point (see tinder, bumble).

That said, women may be in the situation where they like someone and that someone is blind/shy to make the first move (men rarely imagine being the recipient of female attention). I would focus with something where women-only can send a flirt and men can register with the hope of getting one from someone they know.

Best of luck