1- Letspal.com
I think, this is the new founded website. It has 500.000 new users for waiting your message. It is so nice for mobile and desktop. You can chat, share musics, videos and can create polls. In my opinion, website like your city. Describing your city is very easy for this website. You are free for sharing your city information and this is bigger day by day. It has "Travel Guide" module and you can read every information about a city. I was searching all of the features and everything is free. New and best for me.
2- Penpalworld.com
With 2.000.000 members it is big penpal website but i was searching you have only 3 messages limit for free account. You should improve your account for getting the all features. You can search members with country, age also city filters. It is very useful website for a finding penpal.
3- Interpals.net
With 4.000.000 members it is very very big. You feel free for sending messages, visiting profiles. It has not responsive design for mobiles. You can share only 10 profile pictures. And some of features don't work well but it is also useful site for language exchange and chat with a native speaker.
4- Penpalhub.com
This website has mostly United States, Canada, Australia people. Website has 22.500 members from the world. System is very old and generally members are offline but it is very fast website and you can visit members profile quickly.
480.000 members from the world but mostly it has asian people are waiting for your messages. Sharing photos also its feature and everything is free like most other websites. Penpals want to learn your culture in this website don't miss it.
This website's registration step is very long but if you give true information you can find a member what you want also. There are text chat, voice chat and word games and more special modules for learning language.
7- Globalpenfriends.com
If you want to find snail mail people you can use this website. Register for free and there are 300.000 members. It is very old website, In 1995 was founded. You can create your profile very quick and easy. Information section is so clear. Be enjoy there.
8- Penpalschools.com
There are so many teacher waiting your message. 10.000 educators from 170 countries. In my opinion it is nice to learn language and for finding a penpal. As says, there are thousands of people to communicate each other.
You can order an online student letter in this website. So many people can exchange their letter from his/her country to another country. This is the fast and not expensive way to find a penpal or language culture or learning language. When you want to speak native speaker it will be so useful.
10- Penpaloftheweek.com
You can share real letter and administrators choose a letter to world. This is old way but classical method. I prefer for this method many times but i should say this it will be take time to sharing your letter. Please don't forget that.
Conclusion, As you see that there are a lot of sites for finding online penpals. If you want you can choose what you want.
Good Luck !