This is in response to a post on Keepapitchinin, where some commenters asked what to do about the widespread inactivity of single church members ages 18-30. I decided that it merited a response, but I didn't want to threadjack a lovely post by Ardis.
I'm 27 and single, and I've been active ever since I joined the church as a teenager. Prior to my mission, I held several YSA and institute callings where I saw up close and personal the issues faced with rampant inactivity among the YSA age range. (In my stake, we had about 1000 YSAs on the rolls, and there were between 3 and 10 who were active.)
There are a few issues at play here:
First: The late teens and early twenties are a naturally itinerant time in the life of an individual. He or she is embarking on adulthood and has to find out what he or she believes and wants to do in life. This is often accompanied by going off to college or otherwise moving away from parents. Sometimes people slip through the cracks. If someone isn't converted to the gospel, it's easy to stop going when you move.
Second: The church often doesn't know what to do with single people. We're a church of eternal families. This is a central doctrine. It's a beautiful and all-encompassing doctrine, and sometimes in our excitement to proclaim and discuss it, we leave out people who aren't married. When every Relief Society lesson consists of "and here's how we can teach this gospel principle to our children" or "and here's how we can support our husband as he does xyz", it makes things less relevant to unmarried, childless members. Although I haven't attended singles wards, my friends who do have remarked that the lessons seem to be geared toward "all marriage all the time".
Third: In many areas, there is a critical mass problem. There often aren't enough single people, so those who are there feel alienated. Some of this is solved by singles wards, but when the singles wards suck away some of the faithful (usually across stake boundaries), it makes it that much harder for those few of us who stay in the geographic wards. The singles wards contribute to the married members not knowing what to do about single people because they so rarely interact with single people, as they're conveniently quarantined in a social leper colony.
Now that I've laid out what I see to be the problem, I'll propose my solution. Of course, your mileage may vary.
First: Eliminate singles wards. This will powerfully show the single members that we are all a part of Christ's church. There isn't a separate church for married people and single people. Granted, there will be some wards where there still isn't critical mass. If that's the case, designate one ward in the stake as some sort of singles magnet ward. Basically, it's a regular geographic ward (I hate the term "family ward"; it sounds so exclusive) where all single members are invited to attend along with the members within the ward boundaries. There is a ward like that in my area for the 25-45 age group and it seems to work well. (I don't attend as it's not in my stake, but many of my friends are happy about it.)
Second: Give single members meaningful opportunities for service. I can't stress this enough. I've felt most engaged in the church when I have felt that I had something to contribute. I find it tragic that so many singles go without a calling. We can help. Use us! We can teach, we can provide compassionate service, we can be in presidencies, we can help with the music. My favorite calling was nursery leader, which is usually the calling that a single, childless career woman would never be offered, but it was great to be asked to serve.
Third: Ensure that the youth (i.e. YM/YW) are given ample assistance and training in the gospel so that they can develop a personal testimony before they reach the critical YSA years. Personal conversion to the gospel is essential. Someone is much less likely to fall away if he or she has a relationship with God and a burning witness that this is His church.
Fourth: Get to know the singles as people, not as projects. We're not broken. We're fellow saints walking the same path as you. Sure, our life experiences are different, but that's part of the fun. We know things that you don't, and you know things that we don't. We can learn and grow together. Don't pity or patronize us. Sure, I want to get married, but I'm quite happy in my single state. I feel blessed for all of the opportunities God has given me, and if I sat around wallowing in pity and sorrow, I would be guilty of the sin of ingratitude. Please don't make it any harder than it already is.