Speaker and online communicator (7)
I believe the answer is:
tweeter
This clue is a double definition.
'speaker' is the first definition.
(tweeter is a type of loud speaker)
'online communicator' is the second definition.
'and' is the link.
(Other definitions for tweeter that I've seen before include "High-frequency speaker" , "part of speaker" , "piece of hi-fi" , "One may follow another" , "Person sending a messages of fewer than 140 characters" .)