Who is in charge of this site is, at least for now and at least in terms of who you should get in contact with, the Stack Exchange community managers. They are listed here on Meta SE. The most active one so far on this site seems to be Robert Cartaino. The best way to get in contact with them regarding site issues is probably the contact us link which can be found in the footer of every page on this site. Keep in mind that they are somewhat busy, so it may take several days to get a response.
In the relatively near future, pro tempore moderators will be appointed to handle the day-to-day moderation and affairs of this site. That will be the status until we graduate, at which point we will have moderator elections. Community managers are still the people to contact if you need to get in contact with someone at Stack Exchange Inc., but their role is fairly limited and the standards are (in most cases) determined by the community here.
As for MathJax specifically, it was enabled about an hour before you posted this question. See Robert's answer. So you shouldn't need to contact them regarding this.