You do not have a service thas is common across Europe, rather individual services in different countries (and in different languages too). Unfortunately I am not familiar with other countries than Spain.
In Spain we have
www.segundamano.es as the largest advertisement newspaper and website, largely oriented to second hand items (segunda mano = second hand). However I am not sure you could use that to recruit beta testers for your application.
PM me if I can help you with this.