Ive done online dating and had some success. You have to get used to the idea that the woman youve been chatting with may disappear without notice and vice versa. Because of the distance, Online dating is as such where women and men are like disposable trading cards....theres always something bigger and better right around the corner.
If you haven't heard from this person for a while (I'd say around two-three weeks), then simply move on. It's not worth pondering over.