I'd say these sites are acceptable. Plenty of fish and Zoosk are
commonly used. People have found great success with it.
The great thing about Plenty of fish, is that it's not just for people
who are looking for relationships. You can put in your profile that
you're just looking for someone to talk to or looking for some new
friends. Some people who are already in a relationship use Plenty of fish, because they just want to meet new friends.