I have felt like this in the past. II may not have the BEST advice, but what I did was;
Firstly, I tried to make plans with friends, even friends who weren't very close. I became everyone's friend. 'Hey want to come over one eve for a bottle of wine/film/game of monopoly one night?'
It wasn't always brilliant, sometimes I found I didn't get on with them that well-but I also found I really enjoyed chatting to some of them
Used the net a lot! I found online forums for things I was interested in (science, psychology,vegetarian recipes but any will do!), and became an active member.
I found a pay as you go gym and went to that, at least then by the time you're showered and home, the evening is less long.
I made 'dates with myself' when nobody was around. I'd go to bookshops and find a book, then find a nice pub or cafe and get myself a glass of wine or a coffee and just sit and read.
I chatted to people on fb.
I researched stuff online, broadening my knowledge of things which made me feel more confident.
I made a lot of telephone calls. I find friends don't do this as often as they used to!
I hope this helps, if it doesn't, maybe work out what WOULD help you and you may get soem more specific advice?