One tool that I use to keep track of a number of companies, is an online registry of legal documentation. It's called societe.com and you can get company statutes, balance sheets, names of corporate executives, board members (hinting to shareholders), etc.
It costs almost nothing (a few euros) to download the legal documentation off the web site, which is just a scanned version of documents that are compulsory for any company under French law to deposit at the Greffe du Tribunal de Commerce.
As an example here is the entry for the company behind glowria.fr.
A very interesting feature is that you can subscribe to an email alert, whenever any information (or new document is added) for any company. You have to do this for each company you want to track of course. It is very useful to track a whole sector.
Another site providing similar information is Infogreffe. It is usually more accurate (and has an english interface), but somehow I use it less often. Now you won't have the excuse not to monitor your competition.
