I have not worked on a game collaboration, but I have worked on other collaborative projects (comics, anime fansub, etc.) online. The success is, of course, determined by the least productive member. If you have a member who simply will not do their job, you can't finish your project. Because your main method of communication is the internet, someone can suddenly "disappear" and you'll have no idea if they're coming back or not.
Even though I know your question was for the future, here are some things I suggest:
* Set up a forum for your collaboration.
* Get MANY contact info from the members. Have them give you a phone number and have everyone involved trust giving out their phone number. People are more likely to at least respond if they're going to bail if you have their phone number.
* Don't collaborate with someone you wouldn't trust giving your own phone number to. Collaborations require trustworthy people anyway.
* If you're leading the project, give report deadlines... like everyone MUST report their progress twice a week (on specific days, by specific times).
* If you use messengers regularly, try to get everyone to actively keep their messengers on and talk to each other casually. Always ask how the project is coming along and talk about your personal progress. People will work harder if they feel everyone else is working hard, plus they will not want to say "I have done nothing" every time.
In the end, I think it's best to collaborate with people you know, rather than strangers, but it's very possible to collaborate with strangers and complete big projects. Think of anime fansub groups who have oftentimes a separate person do each of these things:
* Rip or find "raw" episodes.
* Typesetting
* Translation
* Quality Checking (usually several people do this)
* Video editing, etc.
* Publishing/distributing/webhosting/whatever
Usually this kind of collaboration would have at least 5-6 people working on it (though some groups "combine" talents and only have a couple people, but still) and they can do like... 200 episodes of some long series and complete their project :) So it is very possible.