This is not actually a plugin, but C++ files to include in your project that automatically reports unit tests to the TeamCity server if run within TeamCity.
The reporting is performed via TeamCity service messages.
Alternatively you can use XML Report Processing to import results from running tests to TeamCity.
It can also be used it for not yet supported frameworks such as CxxTest.
teamcity-boost-1.3.zip for Boost.Test library
teamcity-cppunit-1.3.zip for CppUnit