Is there a way to post a tournament consisting of one's chess.com friends?

yep. create an invite-only tournament. and then use the INVITE TOOL to invite your friends. 

Thanks, but do I have to manually invite each of them or can I automatically invite all my friends?

each

Thank you.  But the other would be better don't you think?

Yes it would Whitebull! 

C'mon WB..  Set up a tourney, I'll join it!

1. Create a group.
2. Persuade all your friends to join it.
3. Create an invitation-only tournament and invite the whole group at a stroke.

(Ref. intra-group-tournament)