Google iOS API thumbnailURL: is not working -

i'm using google api ios app, , have code

    [sharebuilder seturltoshare:[nsurl urlwithstring:@"https://facebook.com/uncollectible"]]; 

that works , embeds url post on google+ expected.

but method deep-link set doesn't:

    [sharebuilder settitle:@"uncollectible"            description:@"stay cool. stay debtless."           thumbnailurl:[nsurl urlwithstring:@"http://facebook.com/uncollectible"]]; 

please advise. thanks!