Sites possibly penalised by Google
 

I wonder if anyone can offer me any pointers?

My sites used to rank very well in Google searches, usually appearing on the first page for the most popular search terms. In the last few months however, they’ve dropped significantly, down to page 6 or lower for many previously high-ranking search terms. Site visits are down accordingly. All seven sites share the same design and general hierarchy, and all link to the same Facebook, Youtube and Twitter pages. The internal URLs are different and the text has been rewritten for each site to avoid duplicate content issues. They all offer the same fundamental products, but there are seven sites to target different keywords.

The sites are on two servers, and all sites have a unique IP address. The IP addresses for the sites on the same server are different in the last octet only.

With recent Google changes in mind, could any of these factors be a possible cause of the drop in Google ranking?