I wasted decades of my life in a similar mindset. It's a poisonous way of thinking and it is a negative feedback loop, it will never get better on its own, the only way out of it is to either decide to take action or to die already.
You have no confidence because you don't believe that you are valuable. The only way to fix this is to convince yourself that you are valuable, to become someone who you believe is valuable. To have self-confidence is to have trust in one's self, there are no shortcuts, you can't fake confidence. There is a paradox in that it would take real confidence to convincingly fake having confidence.
You have to start trying to figure out what you like about yourself before you can expect anyone else to do the same. That starts with learning who you really are, being 100% honest with yourself, taking inventory of your skeletons, and confronting your demons. It's not easy.
One of the best things I think I ever decided to do for myself was to start writing in a journal every day. It is like garbage collection for the mind. It helped me to figure out what I believe, what I fear, what I want, and who I am beneath the facade of defense mechanisms. It's a way to figure out which thoughts are worth holding on to and which are anchors dragging me down, and by writing about them it becomes safe to let those anchors go. If I do ever need them again I now have them written down.
I write about whatever is on my mind, and I write exactly what I think honestly and unfiltered. In order to do this without holding back I had to promise myself that under no circumstances would I allow anybody to ever read my journal, and I had to really mean it. That's when my deepest and darkest thoughts started to come out, many that I didn't even know were there. The thoughts that were so painful or shameful that I had hidden them away in the darkest corners of my mind where I could avoid safely acknowledging them forever. Those are the thoughts you have to deal with to move forward.
Self-confidence is almost a magical thing. Once you really believe that you are someone worth knowing other people will start wanting to know you. Once you begin to figure out what you actually believe you will have something to talk about. Once you are comfortable enough with yourself to stop being intimidated by people and start looking them in the eyes they will respect you and like you and want to be your friend. Once you respect yourself you will lose that desperation for external approval and start standing up for yourself rather than being a pushover. This isn't stuff you learn, it just happens as a side effect of self-confidence.
I would also suggest eating clean and exercising, keep up on your grooming, and wear decent clothes. Looking and feeling good physically will do absolute wonders for your mindset and self image. It also wouldn't hurt to meditate and read every day. Whatever it is just do something to improve yourself, the point is that you have to put some effort into yourself every day if you want other people to give a shit about you. Really, nobody likes self-hating people, and can you blame them?
Good luck man. I know this shit is probably overwhelming and the thoughts of looking at your skeletons and staring down demons stirs some deep anxiety, but you really do have the power to truly transform yourself in a very short period of time. It's really hard to start, but once you get momentum going it becomes impossible to stop. Once you reinflate your spirit and feel like a full human being the thought of going back to the old way will just not be an option.