You can
contact a user by sending him/her a message via different Site pages.
From the "Radar" page: click on the "chat" icon in the
preview of a user's profile. Type your message in the corresponding field and
click on "Send";
From the profile of the person you like: click on the "Chat"
button and type in your message;
Click on the chat icon in the menu bar: you will see active chats, and be
able to manage them, replying or deleting them.