In order to view a list of the packages you installed from AppExchange, Click Your Name | Setup | View Installed Packages. These packages can be either managed or unmanaged.
By clicking on the Package Name (Under the Package Name section), you can view the components of the particular package. If the components of the application (with which you are encountering issues) are listed there, then it is a part of that package. Remember to go through all the Installed Packages as the components could be a part of any installed packages.
Also, in the Installed Package's setup section, you will find the Name of the Publisher listed under the Publisher section. In order to find the best way to contact the Publisher, navigate to: https://appexchange.salesforce.com/
Use the Package Name as the search query and you will see that the AppExchange listing for that package is listed as one of the search results. Click on the result and that will take you to the AppExchange listing page. Here you can see 4 tabs Overview, Details, Reviews, Provider. Click on the "Details" tab to find the apps Support contact information to reach the publisher.
Note: Packages created by Force.com Labs are not supported by Salesforce Support.
Does Salesforce provide support for the third party apps or installed packages?