Just watch for extraverts who have good verbal skills and who are spontaneous. Chances are it is one of ExxP types. Then watch for humor that may be weird, imaginative, breaking some rules / politically incorrect, may be even dark or jerkish aimed at one-uping somebody. Then you know it is someone using Ti, so the person is either ESTP or ENTP. I'm not sure if there is any one particular place you can meet ENTPs. They usually have good verbal skills which they like they use. As all extraverts you can find them in social groups. But because they are NTs their interests do tend to be more technical rather than people-oriented so they are not very extraverted extraverts so to say and can engage in activities on their own not needing to have other people around them. I've met a couple of them in college, had two ENTP bosses also who hired me pretty much on the spot. I also met around a dozen of ENTPs via online games. The combination of competitive environment and some imaginative elements that games can offer seems to draw them in.