If you're a designer looking for a platform to offer your services, I would suggest Fiverr and Upwork, both have huge audiences of people in need of design services and also share your fiver and Upwork account links to your social media accounts and also on LinkedIn..
Yes, these two must be the most popular ones, although lately, I've been hearing it's getting more and more difficult to find a project on Upwork. Good tip for LinkedIn!