Hi Dan,
Typically, once a user was assigned Lync license and everything was set up correctly, his/her contacts could be searched by others.
Since you cannot search any contacts with Lync for Mac, I suggest you try searching and adding contacts via OWA (Outlook Web App). The steps are as below.
1. Log into OWA with your Office 365 account at: Http://mail.office365.com.
2. On the left panel, under Contact List, click Add contact…, the screenshot shows as below.
![]()
3. Search and try to add contacts from the dialog box.
If you can search and add the contacts you want here, please check whether the Lync for Mac works smoothly.
If the issue persists, please let me know which kind of Contacts you want to search and add. Are there any external user contacts, or internal user contacts? Is the opposite site using Lync online or Lync on-premises?
Thanks,
Maggie Li