I'm an introvert too! I feel much better doing things by myself-eating,reading,working, travelling.
Oh, you can try online friends to start! Post to /r/penpals , tell them you need help, somebody to practice with.
I find that when making friends, it is a mutual effort. Friends share and communicate, it's not a one-sided courting. Just staring at someone and hoping they will talk to you won't help, make casual remarks, or compliments(everybody loves compliments. Try 'good job on that __' or 'what are you eating? It smells really good'). They will notice you talking to them, and talk back...back and forth, like a tennis game. In tennis, player A lobs the ball to player B, who has to hit it back to A, then back to B...it takes both players to create a game.
After the first time, do not let it grow cold. Offer them some snacks, show them a funny video, ask them what they did last weekend.
Idea:Maybe at work, buy a box of donuts, put it on the table with a note. Then they may come up to you to say thanks, or you can go up to them and ask them if they liked the donuts. Tell them where you got it from, ask what flavor they like...silly things. Just get a rapport going. Show and tell them what interests you. Ask and listen as well. When they ask you a question, do not just give a dead end reply; answer and then ask them a question (what about you? etc.), when they reply, say what you feel about their answer('wow, really?' 'that's great, I should try that sometime')
I know it's hard. It is harder for me to create and sustain friendships compared to extroverted people. But if you want to have a friend, you have to work for it. Practice conversations and expressions in front of a mirror. Smile when interacting. Maybe don't aim for a close friendship first, try just saying 'good morning!' or 'hi!'. Short phrases.
What type of friend do you feel comfortable with? Maybe find someone who is introverted like you, with similar interests. you may not want a loud and extroverted friend who wants his friends to go clubbing with him everyday.
Try meetup groups in your city. You can pop in whenever, you don't have to see them again if you mess up! They also don't know who you are, so you can start from the ground up. Maybe something like movie or gaming meetups, or art classes. Volunteering at an animal shelter or a charity is nice too, no pressure to interact with others.
Are there meetups and support groups for people with similar issues? Maybe a social anxiety support group?
Wow, this is long, sorry! last advice: Consider talking to your doctor about it, if this is due to excessive anxiety, they do have meds to help.