Where is the message button???

The message button should be above this notification block but it is invisible for basic members.
You'll need a "Pro" membership or "Premium with a free trial" to make it appear and to talk with others.

How to message others?

First send a friendship request to check their interest. 

When they accept you can start writing!

Aspie Singles Notifications Would you like to receive notifications on new messages, friendship requests and so on? No Yes