In the project Europeana Newspapers supported by Europeana and The European Library newspapers from European countries will be digitized or made accessible in one portal. At the project website of Europeana Newspapers you can find more background information. Using the current search interface at The European Library you can already search in nearly 200 newspapers from various European countries held in the collections of major libraries. You can search by title, country, issue date, period and this date in history. As for now the period 1914-1918 is only thinly covered. The project started in 2012 and will be finished in 2017.
Some digitized German newspapers published during the First World War can be found at digiPress: Bayerische Zeitungen. Digitized Belgian newspapers from this period are present at the portal The Belgian War Press. Dutch newspapers can be consulted online at the Delpher portal of the Royal Library, The Hague.