Best Place to Find Freelance/Contractors?

Currently working for an agency as just a regular employee, things have gotten really crazy workload wise where I am at. I just keep getting new clients, and tons of new project hours. I've been tasked by my company to find some form of freelancer or contractor to help fill some of the work-load demand coming in, as they plan to continue to add more work on top of what I am already doing. There are no plans to currently hire anyone permanent. Anyone have any experience in this department? I'm researching Upwork, and freelancer, but concerned it might be similar to Fiver where the majority of stuff here is kind of of BS. Really any insights would help, thanks!