Going to an event where you don't know anyone sucks, but sometimes you have to, like for networking events or work functions where you need to "be seen". Set a 20 minute timer on your phone when you arrive. Knowing there's a clock running will make you more comfortable and give you an out if you're still uncomfortable when your phone vibrates in your pocket. Image from johny.
This isn't a way out of the event, but chances are by the time your 20 minute timer is up, you'll be at ease enough to stay a little longer, or over the initial awkwardness anyway. You can use those 20 minutes to grab a drink, take a look around and talk to a few people you already know, or who look interesting. Knowing that you've given yourself permission to leave after 20 minutes can cut down on that initial anxiety and help you relax. Even if you do end up leaving once your timer is up, you'll at least have made the rounds and given the event a fair shot.
You Can Do It: How to Go to an Event Where You Won't Know Anyone [Apartment Therapy]