I don't know what logging framework liferay uses, but it might not work with logback in the server. It may depend on which dependency/module gets loaded first. For example if liferay loads before logback, then it will likely use the server configuration and not logback. The server will never use the logback configuration.
It's tough to say what the issue might be. By "not showing" do you mean the messages aren't being logged to appenders you have setup in logback or are they not showing up even in the server.log or the console?
James R. Perkins