Good hostel for meeting people in Luang Prabang

I don’t recall seeing any hostel in Luang Prabang. There are all guesthouses and most low end one don’t advertise or online visibility.

http://www.travelfish.org/accommodation/laos/northern_laos/luang_prabang/luang_prabang/all

I would doubt you would have any problem meeting people in LP no matter where you stay.
Last time I was there people just spoke to me whether they were visitors or locals.

Good question, it's something I don't plan for in my trips but maybe I should start doing so, because over the New Year period while in Cambodia I did experience some social activity in a few of the hostels which was nice.

The only thing I can suggest is look through the comments in the hotel booking sites like Agoda etc. I'm a cyclist and get a lot of information from cycling journals, especially accommodation tips so if you've got a particular interest then go search for the blogs that participate in that activity.

The SpicyLaos Backpackers is still there, just under a new name: Lemon Laos Backpackers Hostel

I would love to stay at a hostel that's great to meet fellow travelers at.

You will find the people staying in hostels are travelling, not the locals.