Finding an internship abroad requires your initiative! To find companies, contacts and offers, you'll have to organise your search & answer these questions for yourself first:

• When is the best time for my internship?
• How long do I want my internship to last - min. and max.? (Internships shorter than 3 months may be less interesting for companies.)
• When is my mobility window? What is the earliest start and the latest end? (Think about your modules, exams, etc.)
• What do I want to do? In which direction or field do I want to go with my studies? What are my options?
• What type of fields, methods, technologies am I interested in? In which industries or products is this applied?
• What kind of industries, branches or products do I find interesting?
• Where can I get a good overview if I need some inspiration?

Tip: Visit industrial fairs and trade shows or view their online product and exhibitors lists. Try the Hannover Messe for a start. They have a good exhibitors and product catalogue on their website but also analytica, automatica, ees, embedded world, MedtecLIVE, medical device software development summit...

• Where? Which countries and regions are an option for me personally? Which ones aren't?
• What languages can I already speak or learn? Where will I get by with my language skills? (e.g English works fine in the Netherlands and all over Scandinavia but may not be sufficient during an internship in France.)
• Maybe also: Which regions and countries are particularly known for expertise in a specific field or industry?

You can start your search for companies by looking at the industries and companies of a country or a specific region or city. For a starting point, Wikipedia articles on the country, region or the city often have sections on economy and industry. Often, regions and cities have their own official websites with information about the local economy and industries. There may be company directories for regions or cities.
Each region or city is very likely to have its own chamber of commerce. In many cases, their websites will have a member directory that may be accessible. A few local/regional chambers of commerce offer a placement service.

If you have a bit of spare money, you may want to use the services of a placement agency. The German website of the eurodesk network has a database which lists agencies that offer internship services.