It almost sounds like you are trying to solve the which-came-first-chicken-or-egg problem? You are upset because you are being ignored and you are being ignored because you are upset. You do not reach out and try to get to know others but they are supposed to reach out and try to get to know you.

You have to talk to a person first so they know you are interested; no one can read your mind, even if you are looking friendly; looking friendly and smiling is no guarantee that someone will speak to you, it just makes it easier for the other person to do that "work". But you have to do your part of the work first! If you want to talk to someone, you have to go talk to them, you have to speak, you have to say, "Hey, do you come here often?" or, "Hey, I'm here alone tonight can I hang out with you for a bit; do you know anyone else here?" or, just, "Hey, how are you." Something.

I talk to the bartender (a good idea if you are a girl alone; if you make friends with the bartender and then a guy starts to give you a hard time later, often the bartender will step in and "help" -- police tip) and other people see me actually talking to the bartender and then they enter into the conversation if they can (or I enter into their conversations with the bartender :-)

You have to get the ball rolling yourself. Yes, people will ignore you if you ignore them. That you drink and thus chemically relax enough to feel "good" so you are more approachable should be a lesson in what "can" happen when you are approachable. Next time, rather than think yourself ignored and get angry about it, move closer to people, smile sincerely (knowing if you do so, they might say something to you) and prove to yourself that it is possible for you to be approachable without the chemicals. But don't judge by whether someone talks to you first or not; talk to someone else first and then you'll know if they are interested/not interested in talking to you (which will be about them, not you!).