Is test complet(12.31) will support multi user and multi threads/threading at the same time?

TestComplete interacts with the UI of whatever application is under test.  If you think about it from that perspective, you can't have more than one user using the UI of an application at the same time on the same machine.  This is where the Network Suites feature of TestComplete comes in where you can trigger the execution of different test steps on multiple machines simultaneously. To the extent that multi-threading impacts a single-user access UI, that's the extent that TestComplete supports those things.

if you're looking to do performance or similar testing, that's where either a profiling application like AQTime or a load test application like LoadComplete comes into play.