This post is the first result when we search "owncloud share contacts" on Google. I use OC 7.0.4 and didn't see the share icon too. So i post the "solution" here if some other have the same issue and don't understand why. (so, sorry for the topic dig, but I think this is meanfull)
If you use Adblock, this is probably the cause of this missing icon : Adblock believe this is a "share to ban" (like facebook share for exemple) because of the CSS class name used on the link. This should be corrected in future version of OC, but in 7.0.X, this problem still remain.
Simple solution : inform your users to deactivate Adblock on your Owncloud instance