You can check out www.sheroamssolo.com it is an online travel community for females only. There are travel forums and a community hub where messages are posted, a chat room and more.
Many people use couchsurfing‘s groups for this exact purpose!
I’m in the Georgia and Tbilisi groups and I would say the larger part of the traffic in both groups is travellers wanting to meet up with other travellers at their destination.
Note that you must join each group you wish to read, which of course means you also need to be a member of couchsurfing. (You do not have to be a “verified” member, so you don’t have to pay any money.)
It is not directly related to your question but the www.hostelworld.com website is pretty good at judging hostels’ atmosphere. I just sort the hostels according to rates and choose the one that is not too expensive. It also helps to read some of the reviews themselves.
I chose the hostel that way when I was in Lisbon and I was mainly sitting inside for the whole day talking with the people and barely seeing the city 🙂
Credit:stackoverflow.com‘