Hi Michael,
did you compile using XCode? Or was it make MACOS_BUNDLE? The latter should produce a valid .app (though it might not work 100% of the time, haven't checked recently)
There's also the possibility of using Massimiliano's tm-devel-mac stuff. After some (possibly heavy) tweaking, one ends up with a complete installation from source of all the libraries required for TeXmacs, ready to be used with the ./configure. I must confess that I gave up after many hours of (fruitless) said tweaking, but YMMV.
Cheers,