I know that Xia Lab @ McGill have launched a user-friendly online platform for working with 16S data (http://www.microbiomeanalyst.ca/), although I have never used it.
I frequently use their well-established MetaboAnalyst platform with great success and so I would recommend trying MicrobiomeAnalyst.
The homepage shows a link to Projection with Public Data, in which you should be able to generate PCoAs.