Diagnose Java memory leak

We are using Tomcat and have FusionReactor as a tool to look into the application and memory characteristics. It is running on Java 8 using Concmarksweep. However we notice that the Old Gen growing over time until it eventually crashes with OutofMemory java heap, which leads us to believe there is a memory leak in the application. We need you to help us locate where is the problem code. You may use other tools like Jprofiler or your preferred tools. As this is working on a production server, we need to work closely via teamviewer to diagnose the problem together. It is expected that you have experience with memory dumps.