[Air-L] Effects of perceived social presence in online communication

Hello everyone, I have come across a paper by Kathy J. Lee "What goes around comes around: An analysis of del.icio.us as social space" from 2005 and am very interested in the effects of perceived social presence on bookmarking sites as described in the paper, but also on social network sites etc. I would be greatful for recommendations on further reading. Thank you! Veronika