"Choose your own adventure" is always fun, but it'll get boring if people run out of ideas and don't have anything to do. You should have some kind of over-arching story going on that people can fall back on so they have a sense of progress. Sure,  I can make up my own mini adventure, and I probably will, but when that's done I would like something already built in to work on.

Suggestions:
1. Looming threat of a massive cyber attack that could threaten the internet globally. We have to work on tracking down hackers who are a part of the threat.

2. Looming threat of a massive terror attack that could kill millions of people. We have to hunt down operatives, locate hideouts, track weapon caches, etc. Act either as vigilantes or to steal money from the terrorists. A nice twist on that would be trying to convince the other characters to get involved in the first place. Like, why should I care? That way we can do whatever we want until we decide we want to get involved.

3. Mystery guest leaves clues and starts a massive global scavenger hunt of some kind, with promise of a large cash prize or whatever. That could lead to teamwork and shaky alliances between characters.

Personally I really like 2. Then players can do whatever they like doing towards taking down the terrorist threat (hacking, wet work, theft, counter intelligence, whatever). It could be one big mystery or a series of mass attacks with public warnings. Maybe a bomb could go off and kill one of a character's family. Maybe nothing would happen to affect them and that player decides to do their own thing for the entire RP.

Of course, it's on you to write the story. I'll co-GM if you want help.