Perhaps your ex is trying to avoid you just to see if you really want them back or not.
This may happen to be a psychological behavior adopted by your ex but do not let it put you off.
  If you want them back it is you who will have to make the effort, especially if you are a man and your ex a woman.
She will want to feel sought after and craved.
And if your ex is a man, well, perhaps then too you will have to do the same.
  Phone your ex whenever possible.
Do not leave any stone unturned to get your ex back.
Make phone calls and send messages.
Call them at their home phone at a time when they are likely to be home.
Avoid calling at work because that will cause more trouble for you.
They will avoid your call saying they're busy and cannot be disturbed.
  Be seen around in the places your ex frequents.
Even though you may not be sure where exactly to find your ex on a particular day, you could certainly find out through friends where your ex is on a particular day.
Be around and talk to everyone around but addressing your ex more directly.
Do not feel ignored if your ex does not care to reply you, the others will or will prompt your ex to say something to you.
  Visit your ex or arrange to meet up.
If you already have been used to doing so earlier then visit their place to meet up with them.
Do not feel dejected if your ex does not speak with you for some time yet - you can always carry on conversation indirectly or with the others at home.
If you used to meet up with your ex after work then see that you are around at that time to meet them.
You'll find they'll perhaps accompany you, though in complete silence.