If you feel your birthday is important for a group/event, you might share your birthday to Facebook, Twitter, etc Social Network for your network.
However, you might want to get a wish from Google for your Birthday, you may easily get this done as step below.
1. Log into the Google account with http://www.google.com/profiles/me.
2. Click on the “Contact info”.
3. Select “Edit Profile”.
4. Select your Birthday and save it only. Enjoy