Depending on the culture where you live, you should find interested models in almost every social situation. In three years of shooting primarily offbeat artsy nudes, I've met women socially, on Instagram (probably my easiest space for newcomers) and Model Mayhem (most reliable). Luckily we have a fantastic art model community on the West Coast. One of my early models introduced me to the circuit and I found a half dozen photographers shooting similar styles and realized that they all shot with the same traveling models. After getting a clear idea of the ecosystem, I found myself inspired by the new crop of young female photographers/modelographers and even though I'm old and male have found a lot of new ideas and faces there.
Having a portfolio available on Insta gives you some level of credibility. Be aware that young and amateur models may feel vulnerable -- it's part of your job to put them at ease and just generally not be a creep. I've never encountered a problem being honestly appreciative of someone but the line should, in this day and age, be obvious. It takes some bravery (as a newbie) to talk with your model about what they are comfortable shooting -- do you want a ragged look with a sexy vibe? Talk about it. Do you want "girl next door" innocence? Talk about it. Just a backlit line of hip? You get the idea, right? Honestly, this has helped me with my communication everywhere. And over time I've made some real friends in the community and find the girls referring friends to me because of their positive experiences. Shoot what you LOVE (kink, innocence, lighting...whatever), talk to the girls about it and let them help you achieve your vision and be respectful. Oh, and have some (unopened) soft drinks and fruit available.