You have repented but have you deleted the account at the site in question? Also, you don't have to disclose the details of your sin, as that is disliked in our religion. If Allah kept your sin from becoming public, then you don't need to go do it yourself. I would delete that part of your post if I was you. Though I understand your intentions are noble, that's a very bad idea. In Islam, the ends don't justify the means. For example, I cannot go inside a bar or a club and mingle with the people, maybe even end up having a few drinks myself, because I think I'm there to "make dawah". Same thing applies whether I go inside a strip club, a casino, a movie theater where filthy movies are being shown, etc, with the intention of 'making dawah'... it doesn't matter. The logic is faulty. Even if someone ends up accepting Islam with my so-called dawah at the bar, I highly doubt this would help save me from the fire... if anything, one would probably get closer to the fire by doing this. Allah knows best and may He protect us all, Ameen. What you're proposing is the same concept.