Mostly you don't need to find supervisor for MEng. But some universities made it as compulsory for some programs. So please do check your university website for proper answer.
Are you on a research-based program? If so, you must have one. If you're on a course-based program, I think you wouldn't need a supervisor since you won't be doing any research that needs supervision. And usually for research-based programs, a supervisor is one of the requirements for admission.