Best to make a new thread when you ask for Beta Testers, so that it's really obvious when they visit the forum.
Also remember you'll need to allow a couple of days for everyone to get back to you. Most beta testers sign up, receive their copy of the map, then say something like "oh, I'll have time to play this tomorrow probably." Frustrating. :P Especially when you have a new map almost ready to go, it's very frustrating that they don't share your sense of urgency. But the feedback is crucial, so I have learned to be patient.. :>
Anyway, some beta testers are really awesome, and will get back to you with large amounts of detailed feedback within hours... :>