You can report a player using the in-game "Report User Abuse" Button. This button is located below the chat tabs when they are visible. (see below)
When pressed, the "Report User" window will be displayed. Select the name of the character you wish to report and choose the correct reason. You may also type in a brief description of what is being reported.
You may also report players through the support portal as a ticketed report.
When reporting through a support ticket, any recent video or screenshot evidence must be provided for an investigation to be conducted. Once a report is received, it will be forwarded to the proper channel for investigation. Furthermore, any action taken on the reported player cannot be further discussed, so the ticket will be closed.