TeamCity loads custom plugin, but there's no evidence the plugin code runs
Solution 1:
The website describes it as being easy (yeah, if it works):
1. Shut down TeamCity server.
2. Copy the zip archive with the plugin to <TeamCity Data Directory>/plugins.
3. Start the TeamCity server: the plugin files will be unpacked and processed automatically.
There is also online step-by-step guide on installing TeamCity plugin here.
Solution 2:
You need to use the following code:
Loggers.SERVER.info("Your message");
This will log to teamcity-server.log. Loggers class also contain other static fields like AUTH, VCS and so on. Each corresponds to separate log file (e.g. teamcity-vcs.log, teamcity-auth.log, etc.). In order to use this code you also need to add the following dependency in your pom.xml (for Maven):
<dependency>
<groupId>com.intellij</groupId>
<artifactId>openapi</artifactId>
<version>7.0.3</version>
<scope>provided</scope>
</dependency>
This was tested with Teamcity 8.1.