Very few Folks seem to be interested in "Multiplayer" activities nowadays.
It used to be very popular, and well supported, in the old FS 2002 and FS 2004 days...

...!
Regular daytime and week-end tours, fly-ins and air-shows, etc, were frequently arranged between members on Simviation, using FS 2002 and FS 2004, and much enjoyment was to be had!
But after the appearance of FSX, and all the various problems associated with it, including Multiplayer connections via the dreaded (complicated) "Gamespy", the interest has greatly diminished, and only with the option to connect via "FS Host Client", to the many FS Host Servers, has its popularity become more evident amongst FSX users
There are now a number of FS 2002, FS 2004, and FSX Pilots all happily flying together now, all using the various FS Host Servers every day!
I connect to Multiplayer every day in my FS 2004, (and sometimes/rarely FSX), and either join in, or have other Folks join me, on a number of Multiplayer Sites with no problems, apart from the dreaded "Time Zones"...

...!
FS 2004 and FS Navigator is just as popular in Multiplayer as it ever was, amongst a large number of enthusiasts, as can be seen by the entries on the servers; and the number of FSX Pilots is gradually increasing amongst those who have successfully sorted out the various; "FSX problems"!...

...!
Paul....Multiplaying most days...mostly in Sunny California!...

...!
P.S....I tried Kelvin's link with my FS 2004, and tried to connecting to the Servers, but it looks like its only aimed at FSX users, on a special dedicated Server.
I've always preferred the idea of mixing it, with all the FS 2002, FS 2004, and FSX Pilots, all on-line together. Much more Multi-Ethnic!...

....!