I agree with the last two posters that Yandex is currently one of the best reverse image searches. All the search engines are pretty simple to use so there is no excuse not to use the yourself before making a request. That being said, sometimes you just can't find it and you have hope that someone else might be more lucky. The only thing I would say is to make sure to mention that you already tried searching.
I have found that if you go to Yandex and search it solo and not using the group type searches that are add-ons to FireFox or Chrome it sometimes throws out a different result so it might be worth doing individual searches on the big reverse image searches.
These are the big three:
https://www.google.com/imghp?hl=en&tab=wi (If you click on the little camera icon you can browse to find the pic you want to search.)
https://yandex.com/ (Very simple interface. Click on 'image' and it goes to the reverse image search page. Click on the little camera icon just like you do in Google.)
https://tineye.com/ (Click on the up arrow and find the pic you want to search.)