What should a faculty member outside of the US do to move to a top-tiered American university?
As discussed here (Is it more difficult to score a Tenure Track position in the US when applying from outside?), getting a US tenure track position from e.g., Thailand might be tricky. JeffE pointed out that it is not necessarily impossible, however, your friends would likely need to be on the top of their fields in that case. Your friend from Singapore seems to be a different case, as the universities in Singapore (at least NTU and NUS) have an excellent reputation around here (something that can, unfortunately, not be said about universities in Thailand or Indonesia).

In any case, my tip is to try to get a postdoc position in the US first. Postdocs are often reasonably easy to get into (at least in CS, can't really say for social sciences), and can act as a step ladder of sorts to faculty positions. Anyway, your friends need to be aware that the academic job market is no piece of cake in the US. Hence, no matter what they do, they need to expect that getting a professorship at a top university may simply not work out, so they should have a fallback plan to account for this case.