We have removed this feature in PubCoder 4 since it was limited to certain services and users prefer to handle this on their own.
As an alternative, you can easily use ShareThis or similar services and embed the sharing code in-page. Using ShareThis in PubCoder is a two-step process: simply paste the buttons code in a Smart Object:
<div class="sharethis-inline-share-buttons" data-url="https://pubcoder.com" data-title="Sharing is great!"></div>
and import the ShareThis library in Code → Project → HTML Head:
Be sure to change the property value with the one for your own sharethis account.
Here's an example project for this: https://www.dropbox.com/s/l37opkazpejhulq/sharethis-example.pubcoder?dl=1