FRANKFURT—European auto makers have plowed tens of billions of dollars into developing electric cars and hybrids to comply with stricter restrictions on tailpipe emissions. Now they face the challenge of selling those vehicles.

Volkswagen AG, Porsche and Daimler AG’s Mercedes-Benz all unveiled electric models at this week’s Frankfurt auto show that will be heading to dealerships soon. Executives said more hybrid and plug-in models were on the way, as part of a broader push to electrify large parts of their lineups.

However,...