The contact management in normal Google and Google Apps accounts is somewhat painful as it does not necessarily work as expected – tips on how to get it working are e.g. available on lifehacker.com.
If you use OSX & iOS and have ever suffered from disappearing contacts, here is what you can do:
1. login to the webinterface of your Google account go to the ‘Other Contacts’ Group – most likely this is where your contacts have moved to. Select them all and via the Groups button move them back to the ‘My Contacts’ Group;
2. to prevent this happening in future go to Settings > General and under ‘Create Contacts for auto-complete’ choose ‘I’ll add contacts myself’;
3. on a mac with OSX open Contacts and resync, the missing contacts should reappear;
4. on iOS devices go to Settings > Mail, Contacs, Calendars select your Google Contacts account, switch it OFF, press DONE, then switch it ON, press DONE again… next go to Contacts and check they all come back again.
Obviously the above only works if the contacts have not been deleted.