You've come across a Facebook post that you want to share, but there's no share button like there usually is. There are several potential reasons why a share button might not be available on your Facebook posts or those of other people. Most potential causes can be fixed either by you or the other person.
How to Make a Facebook Post Shareable
If Facebook friends tell you that they have tried to share one of your posts but cannot, you probably need to tweak your privacy settings to make sharing possible. Facebook's privacy settings control every aspect of your profile from who can see your photos to who can see posts you make. You can change privacy settings on an individual post that you want to make shareable by clicking the "Privacy" icon next to the post time stamp and selecting either "Friends" or "Public." Select "Friends" if you want friends to be able to share the post or select "Public" if you want anyone to be able to see the post.
You can change your privacy settings for future posts by clicking the drop-down arrow in the top right corner of Facebook and selecting "Settings" and then "Privacy." Click "Who can see your future posts" and select "Friends" to make all future posts shareable by your friends. You can change this setting at any time by revisiting the Privacy section.
Sharing Posts From Pages
Facebook Pages are completely public and can be viewed by anyone even if they have not liked the Page. This means that the Page's posts are also public and can be shared by anyone. You can share a post from a Facebook page by clicking or tapping "Share" underneath the post and then typing in a message to accompany the shared post if you desire. Tap or click "Share Now" to share that post with your Facebook friends.
Sharing Posts From Groups
Facebook groups can be either public or private, and this affects whether Facebook posts from the group are shareable. Public Facebook groups are fully open to everyone on Facebook, even those who are not members. You can share Facebook posts from public groups by clicking or tapping "Share" below the post. If the Facebook group is private, you can only share posts from the group with fellow members of that group.
Sharing Posts From Friends
Whether or not you can share a friend's post on Facebook depends entirely on that friend's privacy settings. If you do not see the Share button below a friend's Facebook post, their profile is probably locked down. You can't share their posts, although you can ask a friend to change the privacy settings on a post to "Friends" to allow you and others to share the post.