They might - it depends on what is going on in you. I wouldn't rely on them as a sole or primary treatment.
Note that this is all for constipation-type, I fortunately don't have experience with mixed, diarrhoea, or the type with serious pain.
If you have a good doctor that should be your first resource, but you might not. I swore off GIs after my experience- a variant of "you're not dying, deal with it and quit bugging me" combined with a very poor handling of a drug allergy issue that could have gone very badly.
You're probably ready to punch anyone who tells you "eat more fiber," (along with "it's in your head - just think positive and it will go away"), but the fiber part is important. It doesn't eliminate or even significantly reduce my symptoms, but it does help a bit and is completely safe. YMMV - on some people it seems to clear things up.
Not sure about diet - again it seems to help some people, but no change on me. I avoid any book where someone has a "guaranteed program" because they've never worked for me.
Apart from the fiber I have a "menu" that I rotate around. Mirilax for a while (there are some warnings about long term and high dose use on the back, and since I'm over the recommended dose when I'm on it I try to give myself time off it), enemas when necessary. Stimulants sort of scare me - it's probably irrational, but I worry about "breaking" things worse.
If you're going to try other-than-Mirilax oral laxatives do yourself a favor and try them out when you don't need to do anything for over a day. I have found they are very unpredictable on me, so I stay far away because my work has limited restroom opportunities.
I am a bit surprised that there isn't more on enemas for this, given that getting crap out is what they're good for. You see unsubstantiated stuff on "cure cancer" "stop acne" and other types of things, but little on IBS.
NOTE: VERY IMPORTANT!!! Do stop to make sure you know what you're doing before trying enemas! You can seriously injure or kill yourself if you aren't reasonably careful. I looked into it before deciding to incorporate them. The biggest risks are physically damaging your rectum, using a dangerous/stupid solution, or having a preexisting problem (kidney issues, weak intestine - if you have either of these do talk to your doctor). They can be safe if you are careful with the nozzle (don't force, use a soft tube if there's any question, don't put in too far), and be careful what you put in the enema (big problems with things such as scalding water, hydrogen peroxide, Hibiclens (!), and other stuff. For IBS start as gentle as possible - too much and your colon might get back at you.