Ever since I could remember, I feared talking to strangers. My anxiety and discomfort arose from the idea of interacting with people I didn't know, which was totally awful because I am an extrovert and love being around people; but, the idea of interacting with new people, whether it was alone or with others was a completely different thing.
The thing with social anxiety is that it can hit anyone. Whether they are introverted or extroverted, it doesn't matter. People always assume that if social anxiety exists, it's some quirky trait of the introvert who sits all day reading books. They never assume that the person chatting everyone up at the group gathering could also suffer from the same anxiety. Everyone has always told me that I talk a lot and that I am a very outgoing person, but what they've never seemed to notice is that I am uncomfortable around new people and acquaintances about 250% of the time. The term "diarrhea of the mouth" is something that all of us extroverted, socially anxious people can understand. There's this thing about silence that's nerve-wracking, as if everyone can pierce their gaze and read you mind, so you must keep talking. You must fill any gap that could be left, and when the person interjects, that's fine, but there cannot be silence ever. When you talk you must keep going because every word feels wrong and somehow by ranting or continuing with your speech, you can try to ignore what the other person could be possibly thinking. You know what you're doing and your brain is telling you, "Oh god, you're making an idiot of yourself. Shut up!" but this diarrhea of the mouth is your only defense and so you keep going and going, until finally the person talks to you, or the conversation ends. It's not that I want to control the conversation, that I am evenly necessarily over talkative, I just feel somehow safe by the confines of my ranting. As safe as you could be in a cave full of sleeping wolves, but at least they're asleep and not aware of your presence, right?
Another big issue with the extrovert who is also socially anxious is that the idea of the center of attention is a double-edged sword. You like attention; it gives you a chance to interact with people so you can feel energized. But at the same time, being the center of attention makes you realize there are lots of eyeballs staring at you. Lots of brains thinking and judging you. It's gets hard to tell then if interacting with people gives you energy sometimes because the anxiety can literally almost fully negate all the energy you have gathered. Which means you need to be alone to relieve the energy from stress. but at the same time people don't understand why you need to be alone. You're the life of the party, after all! Also, your body doesn't seem to understand that trying to relieve anxiety can also deplete your energy because now you aren't around people being stimulated as you usually are. It's a constant battle between how much social interaction is enough. You need to be around people, but you also need to be aware of the stress it may include.
This is why usually I can relate to introverts or the ambivert in the fact that a few close friends is enough interaction, but for the extrovert, sometimes, we have to meet new people to get more energy. It's like you get used to your best friend's energy levels and have to find a new one. Like a junkie. What's there to do then? If a situation of common interest is at play, usually I can feel more at ease with the general public; but, there's still criteria I must work through to fight my anxiety. It must be on certain grounds, and even if the diarrhea of the mouth never stops, the obsessive tendency to yell at myself internally for talking is always there, but it's at a more manageable level. It's easier to work with than say talking to a cashier, a stranger on the street, a random kid in your college class, etc.
I honestly wish that there was a way for people to understand social anxiety in the extrovert. We are not some quirky fad. We are not those introverted bookish nerd that you think. We can be extroverts, people of any age, any profession, any religion, etc. It is a mental illness like any other type of anxiety or disorder. It effects our lives in ways we cannot fully control. It's not something we can fight by interacting with people more or by shoving the person into the situation you're scared of (I am writing directly at my parents who have tried to force me to buy my own purchases at the cashier when I was young). It's something that the individual must work on at their own pace, at their own comfort level. All we need is love and understanding.
So please, understand that the talkative girl at the party, or the bookish nerd who always sits alone at the cafe could both be suffering from the same type of crippling anxiety. It shows in different ways, a we are all unique people with a common disorder.