Beach/party destinations in europe?

Myself and a mate (both male/18) are going interrailing round europe this summer. We were planning to head from amsterdam to istanbul on roughly the orient express route but have just realised we havent included any beach time. Any ideas for a good place to stop off? We are looking for a good party atmosphere with plenty of young people to hang out/party with - we had initially thought south of spain but thats a bit of a way away so I thought some of you lovely people might know somewhere closer to our route - i personally was thinking italy/croatia sort of thing - not greece as the strikes at the moment will really threaten train services. Specific towns would be appreciated rather than general areas but areas are also okay. Please bear in mind this is on a budget as well! Cheers.