It all depends on your looks. In most cases, if you went into a public place with lots of guys and just raised your voice and said "Hey everyone, I'm single and I want a boyfriend. Here's a paper if you want to put your name and number to take me out." I bet you would have at least 10% to 20% of the guys signing up.
It really is that easy, if you are hot. If not, then I don't know what to tell you.
OR, if you are into video games, just hang out in a gamestop and ask out a guy customer there. Lots of them would say yes.
Maybe you give out all the wrong signals or don't realise when men are into you. I can't give advice on being approachable because I've yet to manage it consciously but I can identify when guys like you...
They check you out when they think you won't notice, their eyes are drawn to your lips or your figure, they get tongue-tied around you, they make suggestive jokes in the hope you laugh, they make excuses to talk to you/hang out with you, they defend you a lot or give caring gestures.
Online dating websites. Tinder for sex hookups, pay websites for long-term relationships. Usually, though, the pay websites will have a free option with diminished utility.
I would suggest eHarmony. I met my soon to be wife there. One rule: be truthful to yourself and to the other person, and come out and just say what you want and what you are not willing to put up with.