Missing friend

It is impossible to tell from your opening essay whether your friend has been sleeping rough or abusing drugs or really in serious need of mental/medical help.

Other than the fact he has been out of contact with you and may be gambling, could you tell from your brief recent meeting how has he been keeping?
Is he physically fit and does he have a place to stay?

I don't think it is helpful to start a forum thread unbeknownst to your friend unless he is immediately imperilled.

Hard as it may be, above exclusions permitted, you should leave him to lead his own life.

No, That isn't helpful and unnecessary^.

A guy is missing when everyone in their immediate circle hasn't heard from him for a good 6 months. Also when the last time people saw him he wasn't in the right frame of mind. Plus it seems everyone on this forum seems to have an eye for spotting strangers riding around town on bikes then maybe they'll be able spot Nigel.