Tiki Social Networks is an advanced feature; therefore, you'll have to set the preference switch to "Advanced" (from Tiki 16) or check the "Advanced" checkbox in the filter preference menu (prior to Tiki 16). Note, you may want to set Advanced as the default in the preferences filter menu so you can always see the advanced features of Tiki.
To activate the feature, go to Control Panels, and then Features. Look for the "Interaction with online services or other software" section and enable "Social networks". You will then have access to the "Social networks" panel and be able to configure everything from there.