Considering that a church is a congregation (a group of believers, commonly referring Christians), a church doesn't need a building or physical location. Understanding the latter, the concept of an "on-line church" may exist. Of course, understanding the idea that this "church" is in cyberspace (internet, in the web, merely housed in a server somewhere) and built with bits and bytes is a difficult concept to accept.
Does this mean that we could pray to God while visiting a web server? Yes, as a matter of fact, we can and should pray anywhere.
Does this mean that we could be part of a congregation? Yes, we don't need to see a person's face to look into his/her soul.
Now does mean that a pastor would deliver a sermon? Yes, of course, we're all ministers of faith. We can deliver a sermon although a "real" pastor would do a much better job.
Could a pastor deliver pastoral care? Yes, the job of a pastor never ends. A good number of pastors nowadays have email accounts and can reach anyone anywhere at any time.
Considering and/or understanding all this, the website of any "real" church is an extension of that church and faith. Anyone can be part of that "real" church going to that church website and listening to recordings of the sermons (something many churches do nowadays).
By taking this same concept backwards, a church website (an on-line) church may exist although it lacks a building where the congregation could meet and pray in person. Look at the list of some on-line churches below.
LifeChurch.tv
http://www.lifechurch.tv/
Church of Fools (Methodist Church)
http://www.churchoffools.com/
Cyber-Church
http://www.cyber-church.com/
