I am not familiar with what sort of data Google Ads or Facebook needs, but I suspect that segments won't work?
I don't have Audience Manager either, but I suspect that though Audience Manager would use segmentation to define user groups, the audience would more be stored for sharing as something more like a list of User Ids that were returned by a segment... so that Google Ads and Facebook could say "Audience X" are these IDs, and "Audience Y" are those IDs, etc....
Segments are more like an actual SQL Query, the logic to return data sets from the Adobe Analytics data base...
However, depending on what sort of import processes Google Ads and Facebook have, you might be able to use Segments to get a list of users (maybe by ECIDs assuming you are tracking your ECIDs in a dimension that you can export, or some other identifier that Google/Facebook can read....) , then you could manually create a process to create audiences in those systems based on the users that you have identified?
I am not sure how often you would have to do this process to update your audiences.. Someone else may have more / better thoughts on this...