P. Hackney and M. Robertson, On the Category of Props. Applied Categorical Structures: DOI 10.1007/s10485-014-9369-4. arXiv version.
M. Robertson, The Homotopy Theory of Simplicially Enriched Multicategories. arXiv version. Part of my Ph.D thesis. This result was independently obtained by Ieke Moerdijk and Denis-Charles Cisinski in their paper http://arxiv.org/abs/1109.1004.
M. Robertson, Spaces of Operad Structures. arXiv version. (Replacement in progress)