Looking for a new trail to ride? I find new trails by using Trail Link or google maps. Trail link is a great database of trails across the country. The primary limitation of trail link is that its mission is to help people find trails for commuting purposes. My experience is that most of the users of the site are looking for new places for recreation. Since their focus is on commuting there are excellent trails that are not included. You may submit trails that are not listed for possible inclusion. I have done this a few times and some of my suggestions have been listed but some have not met their criteria and were not listed.
Google maps is an often overlooked resource. Most people are familiar with the traffic feature on Google maps. If you scroll down a bit further you will find a bicycle feature. This highlights bike trails and bike friendly roads. Much of the data for the bike trails originated with trail link but Google has added to this and includes many trails not listed in trail link. Unfortunately there are bike trails shown on Google that simply do not exist. I would not plan a trip based solely on a bike path shown on Google.
The better trails are named and names may be seen on Google maps if you zoom in. Once you find the name of a trail you may like to visit, do an internet search for that name. Many of the longer trails have their own web sites. Additionally, at the top of the search results click on news. This will search for news articles that mention the trail. Since there is much activity expanding and improving trails news articles are often the best source of the latest information about current status of trails. If you decide to visit a new trail you may want to return to Google maps/bike paths. Find the trail again then change the background to satellite. This will allow you to locate parking adjacent to the trail. Click on the parking and get directions right to the spot. Alternately do this on your phone and get turn by turn navigation.
Don't forget social information such as actually talking to other riders you meet on a trail. When you stop for a break try to do so where there are other riders. Strike up a conversation. This is often a source for good trail information. Of course Facebook is also a good way to get information from other riders. Look for groups dedicated to bike riding or trail users. In eastern Pennsylvania there is a rider's group called "We Like Bikes" with most of the active members from the Lehigh Valley. There is also a group of trail users for the "Pine Creek Trail".
You could also check out twitter, Instagram and other apps. A friend from We Like Bikes has a huge collection of photos on Flicker. Check out Easy Biker. Local bike shops generally know about trails in their area and it is advisable to check with one before planning a long trip centered on a particular trail. If you do travel, there are many outfitters specializing in cycling vacations. These outfitters generally offer bike rentals and shuttle services. Many also offer organized rides with one or more guides, SAG support and lodging (or camping) along the way.