-lxx causes the linker to look first for libxx.so and then libxx.a, unless you override that default by specifying the appropriate actions. In this case, with -lboost_thread, it's going to look for libboost_thread.so and then libboost_thread.a. However, neither of them exists - instead, you have libboost_thread.so.1. Create a symbolic link in /usr/lib named libboost_thread.so to libboost_thread.so.1, and you should be OK.
For example, execute the following commands:
su (must be logged in as root)
cd /usr/bin
ln -s libboost_thread.so.1 libboost_thread.so