As Reggie was saying, they are not "social", but they are also tolerant of one another IF (huge if) there are ample resources for both animals...
I suggest NOT housing two Tegus together unless doing so in a HUGE (6'x12') enclosure. While they do generally tolerate each other very well, the stronger animal will naturally take the best of everything. Therefore it is only "right" to keep a pair together if there are two of the best of everything. For example, if there is one basking spot and the stronger Tegu is enjoying it, if the lesser Tegu crawls on top of him to enjoy it, a territorial battle could easily break out. The same could be said of water, burrows or anything...
I would consider my Tegu 'social' in regards to getting attention from me, the owner. I often let my Tegu free roam in the house and while he will explore everywhere he has access to, he will also come to where I am sitting and 'visit' me frequently. Sometimes simply crawling over me and continueing on, sometimes stopping in my lap to hang out. Previously my father insisted he only stopped on my lap for the heat, until he was able to whitness it a couple of times himself and he admitted the Tegu was obvisouly stopping to 'visit'.
Also, if I go into his outdoor enclosure, almost every time he will come over to me. If I'm sitting or squating he will crawl into my lap and if I'm standing he will try to climb my leg (though he doesn't try to climb other things). I should also note this has nothing to do with a desire for food. If I stay in his outdoor enclosure while he eats, he will almost always leave the food dish (when finished eating) and come over to me...
Back to the enclsoure set up itself... I do suggest using something to break lines of sight from one area to another. In a big empty box a Tegu can easily survey his environment from any place in the enclosure. If there are areas he cannot see, he is likely to go over there to explore. This helps prevent them from becoming overly lazy.
A Tegu takes a lot of investment in both time and space. It's surely not the right animal for everyone. But, if you are willing to give them ample space and sufficient attention, they make amazing pets...