I remembered that i had written an essay (2010) on the issue of intra-EU trade and its connection to the implementation of the common currency. You may read the entire essay here.
My main points were:
1) The basic economic gains from the Economic Monetary Unions and hence the Euro zone were the elimination of the transaction costs, the exchange rate certainty that comes with a single currency, and the price transparency since the consumer can compare national with foreign (within the Euro area) prices more easily. As was explained, all lead to a possible increase in trade since these parameters affect the economic environment in a positive way allowing space for extra trading activity.
2) The prevailing dimension is that Euro does have a positive effect on trade among the Euro zone countries but this is NOT as high as
Rose forecasted (maximum 15 to 20 percent in the long run) and thus the gains from an increase in trade should not be a unique reason for a country to enter the euro area.
3) it was found that entering the euro zone leads to trade creation (not diversion).
4) Lastly, should be noted that although evidence shows a certain increase in trade after the adoption of the Euro among the Euro zone countries, has not been clarified whether this phenomenon is solely caused by the Euro or other policies that led to the establishment of the European Monetary Union.
5) Hence, our main consensus is that Euro should lead to a limited increase in trade among participant countries but is not statistically significant that the main reason for this increase is the introduction of the common currency.
Hence, given the observations that I made on the essay, intra-EU trade seems to be affected slightly positively by the introduction of the European currency while even that is argued by some economists.
The truth about the euro is that only core euro zone states like Germany (and even perhaps only Germany) are expanding exports to the other euro allies. The latter (especially those at the periphery) who tend to be less competitive for the beginning of the euro advventure find themeslves losing exports to other euro states.