It's been forever since I've checked up on it, but Peter & Company is one of my favorite webcomics. Wouldn't recommend if you don't like anthro animals, though.

Pretty much the story is about a highschool age cat who gets this imaginary friend like guardian angel who only him and anyone else with a guardian angel can see and hear. There are, from what I remember, some more serious comics, but it, from what I remember, is pretty lighthearted.

Just checked their official website to get the link and they've been slowly continuing the series. Latest update was March this year, so I don't think it's quite dead yet.

There's also a sequel series ( Peter & Whitney ) that I have no idea about since I haven't read much of it that follows the main character of the original and has him as an adult.

Edit:

The second comic tells you he's twelve year old by the time the story starts, so my comment about him being highschool age isn't necessarily correct...