How to remind people / (ex) co-workers who forgot to reply to a personal note?
This is more or less the heart of the problem. It's about a non-business related matter in a professional setting, because they most probalby get your message while at work, and still see you as a co-worker. In this situation, I use the "TOROFAI" method (Tell Once / Remind Once / Forget About It). Give people a chance to say no without being rude, or forget about it.
What does that mean? As it's not business-related, and because they interacted with you at the workplace (and can still see you as a "co-woker"), people can react like:
- I haven't seen it / forgot about it -> hence, the reminder.
- It's not important right now (and piled up at the bottom of the stack) -> hence, the reminder.
- I don't want to answer (means "no, I'm not interested, but don't want to tell them / want them to forget about it / want them to not ask again") -> hence, the forget-about-it part.
What's important is to not bother them, and don't wait for an answer, as they may not be willing to. If you really want to softly push for an answer, give them an opportunity to deflect. I'd ask them, the first time (or as a reminder, but better at the very beginning), if they want to come out for lunch on day D / Time T. Maybe you've been too broad, and people may not have time to deal with unclear question.
When specifying the day/hour, you let them find an excuse about the job, so that they can use a little white lie (that you'll have to interpret as such) without (they think...) hurting you.
I've done that many time in big companies, and/or with people I wanted to keep in touch with (don't burn bridges), and always got my answer, be it said/written or untold. Hope that you can read the signs though :)