Is there any way to fly missions in multiplayer?

[Fidel]

As far as I know the single player missions can't be played in multiplayer, but has anyone figured out how to import or create any other type of mission? I enjoy flying around with friends, but it would be nice if we didn't have to make up our own scenarios.

[Licopolis]

As far as I heard, missions can't be played in multiplayer (apart from maybe air races but that's whole separate type of missions).

As for the way for "spicing up the flight a little", there are FSEconomy (free) and FSPassengers (paid). I don't use the last one so maybe some other person could prove me right or wrong, but it's experience could be shareable.
As for FS Economy, it does support own FSX multiplayer without time compression. We have made a test flight in A-26 in January 2018, everything went OK. Only one person should be running FS Economy client for this shared flight.

Regarding FSEconomy itself, this addon (or should I say, virtual flying community, or maybe "flight sim outlaws"?) is about patience. You register on the forums and are given about 24 to 72 hours to read the manual while they create account details for FS Economy Gaming World.
We tried to recruit people to our small flying group within FSE but they eventually left without notice, even not lasted enough to see gaming account being made.

What do you get with FS Economy? In terms of gameplay, not much: the needs for planning the flight carefully, weight restrictions, fuel, maintenance and other operating costs, virtual property, and what's probably most important, passengers and cargo waiting for you to ferry them around in almost every airport on Earth. Some of the assignments are made by system itself. Players who had built properties can generate own custom assignments with passenger terminals (destination and amount of passengers in the stack are controllable).
But all that fades when you realize that with FSEconomy you're entering rather mature and friendly community. FSEconomy is governed by a Board, have own club magazine, and various flying groups exist within this club, some of them created to just share aircrafts and others functioning like virtual airlines.

[CougarPleaser]

I've flow FsEconomy for quite a while.

In a nut shell you look thru a list of jobs and accept the ones you want. You can string them together taking passengers and cargo to different airports along the way but can not overload your airplane.