Stop trying. This might make you appear 'needy' and will either scare people away or attract the wrong type of (predatory) person entirely. Lower expectations = less disappointment.
When I was your age I found it easier to make and maintain friendships with people who were older than me, but I had access to a wider range of people due to my part-time job. I didn't find it that difficult to make friends at school or college, but I was never satisfied with these friendships and they always felt very artificial.
Friends of the opposite sex were a different subject altogether. I desperately wanted a girlfriend at that age, and it was obvious. While I could be aloof and feign 'cool' with my male peers, I appeared very needy to girls. It took me until my mid-twenties to get over that - well, to get over myself - and stop caring. As soon as this happened, women started noticing me.
Another thing I'd add as well - expect friends to come and go, especially at your age.