They are both correct sentences, but the best option here is "Who introduced this website to you?" because, by definition, you can only be introduced to something once. Because the period of time in which the event occurred has ended, you should use the past simple tense.
"Who has introduced this website to you" sounds like someone is asking "Who has introduced it to you so far?", as if they are expecting more people to introduce it to you in the future. This doesn't really make sense.