In American English, people would ask, "How did you find me?" when asking someone how they located you, for example: "How did you find me? Did you use Google Maps, a Navigator app, the telephone directory?" In American English, it would only be a very unusual and specific reason for asking, "How have you found me?" An example might be: "I am finished with the interview for the job. How have you found me? Do you find me qualified to start work, or do I need additional job skills?" As you can see, it would be really unusual in American English to use "How have you found me?"

There basically is no difference...the first one, however, sounds more common