Ask your flank what they're doing, then tell them what to do.

I would either force them to talk, or replace them, sometimes calls are better than DM

yell at the flank

http://www.teamfortress.tv/9052/hoolis-team-cohesion-guide#2
let them read through this

I've had similar experiences with silent teammates when maincalling on roamer. The most effective strategy I've found on my end is to ask for information. "Where is their demo?" "Where is their combo rolling out?" "Call focus fire." "Which Uber is better?" "Are we staying or leaving?" "What are Uber advantages?" Obviously this is a lot easier on pocket than roamer since you can see a lot more.

It's kind of a stopgap solution though - your teammates should be offering this information on their own, and asking them for it means that you will waste time and advantages will slip away.

The easiest solution is to just impress upon them the importance of communication and exactly why you feel frustrated as a decision maker without access to as much information as possible. Make sure you do so in a way that is not accusatory or they will get defensive and consequently become less malleable.

It helps to know why they don't do it. Often new players just don't know what to say. Sometimes they can't handle talking and DMing at the same time. Sometimes their mic is too quiet or their voice activation thresholds are too high. Sometimes they're shy and need time to adjust to a new group of people.

And sometimes they just don't talk.

It helps to know this because how much time it will take to get them to talk, if they ever will change, is a big deal to a team who plays a match every week. Is it worth the time investment to get them to eventually talk? Or should you cut them and look for replacements? And that changes with every team, especially when you have to weigh how important winning is to you as a team compared to playing with friends.

Hello,

I've mentored a few teams in this situation. Magically when I the mentor regurgitate how the main caller/leader feels as if it's my own idea, the team tends to change on a dime. Maybe consider having a higher leveled player temporarily mentor you guys. It's always nice hearing someone else's perspective. I know it's sad, but sometimes it takes someone with a little more experience and more respect throughout the community to get it through the teams heads. It definitely doesn't hurt to. There are always players willing to mentor teams! I being one of them.

Best of luck my friend,

Stevokenivo

Em,recruit teammates that are actually social and easy going?

This is amazing

I'll try to figure this out more from now on, I get the feeling we can make a lot of progress this way. Also thanks for the in depth answer, there's a lot of useful advice for me here that I'll put to use :)

They are, but so far it hasn't translated into their comms as well as I'd like

being social or vocal in a conversation (viper) doesn't translate into being a teammate who comms (viper). If anything, they could be counter productive. Someone who talks a lot naturally might have a tendency to either not censor their speech and clutter comms or might avoid comming as an attempt to avoid that

just blame them for anything that goes wrong because you don't know what they're doing

i want to win not feel better about myself

ideally everyone comms but you don't have to have perfect communication with your flank to play at a high level. what you have to understand is that the combo is the center of the team and the flank makes decisions based on what the combo is doing. sometimes the combo will make decisions based on the flank (like the example you gave where your flank is hurt or another example where your flank is bombing/sacrificing in and you can peek for some spam) but for the most part your flank will be making decisions based off of what you tell them you're doing as the combo. at the bare minimum the flank should raise the alarm if something is going wrong but if there's no pressing matters there then you can get away with minimal flank comms.

I think it's too easy to blame your flank for your mistakes. if you're consistently getting caught out and you blame your flank for not helping you position correctly, you're probably just not thinking far enough ahead and can make the right decisions on your own by hitting tab or keeping track of ubers (aka playing faster aka making quicker rotations).

My goal isn't to blame the flank, I'm just looking for advice to what I can do to limit my own mistakes and win more as a team, given the situation. So far I've gotten a lot of great responses which we've started trying to put into action already, so thank you to everybody! I think the flank doing things based on combo / vice versa description is another one of those, I'll try keeping track of the game with that in mind more.

Start doing more flank based ubers like scout + demo or pocket + scout.
Ideally, you want to uber demo + scout when you push last with uber advantage because you should be expecting a sentry and/or a pyro and have your scout call focus for your demo and call where the sentry is etc.

So, a few things.

1. Sometimes, especially on newer teams, the "flank" as it were players don't really know what sort of things they're supposed to say. To start with I'd at least ask them to say whenever they're going to try to take a fight with somebody. Some flanks don't really need to talk to each other that much if they've got a modicum of experience and synergy between the roamer and the scout that hangs with him more in hold situations. The important thing is if they're going to go in to take a fight they need to let the rest of the team know because you could try to help them by being aggressive yourselves or at least trying to distract - they'll also know they may need to back up to a more defensive position should you die - instead of it just happening suddenly. The combo also needs to help them by making it EXCEEDINGLY clear when they need to play as carefully as possible (uber disadvantage/focusing on building/large uber advantage which is about to be used).

2. Your flank should know that it's not allowed to push in most scenarios and they don't get to feed whenever they want - it helps to be condescending "thanks for the feed" getting really close to your mic and saying "solid feed team" and things like that may help to condition them - Pavlovian style - to not do silly things - if that's what your problem is. Your flank holds should mostly revolve around one player baiting another - either the scout pushes up a bit to try to get somebody to chase him around a corner whereupon a roamer shoots the ground 4 times and deftly kills said chasing thing. Or the roamer spams rockets close to a door, and runs away when trouble shows up into his +forwarding scout friend who then gets the kill. Sometimes accidents happen and players die in these scenarios, but it's good to *at least* let the combo know something like that is going down.

3. If you really want to break the spirit of your flank and possibly your combo too you should start running kritz whenever it makes sense to do so in scrims (basically whenever your medic and their medic die in the same fight, but yours happens to die first and a few other more specific situations). Why kritz? Well, since nobody will be invincible it forces your flank and combo players to be a lot more coordinated in how they approach an attack (assuming you prefer not to fail and lose) - so it gets them used to working together. Do we bomb in the roamer first to distract prior to the kritz being popped? If so what do the scout(s) on the flank do? When do they come in or run away, what sorts of things will the combo players say to let them know if/when they should come in or run away? The other important thing about kritz is that you have to do things very quickly - because if you take too long to actually use the kritz your opponents will have uber, and assuming they have the awareness of most plant-life forms, they'll be able to use said uber and nullify your kritz and you're far more likely to get wiped. Plus, if you actually get acclimated to running kritz it provides you with a useful tool/trick you can use in matches.